By JOSÉ DE CÓRDOBA and JAY SOLOMON

BOGOTÁ, Colombia -- A cache of controversial computer files closely tying Venezuela's President Hugo Chávez to communist rebels seeking to topple Colombia's government appear to be authentic, U.S. intelligence officials say.

The trove -- found on a dead guerrilla leader's laptops during a military raid in March -- is likely to ratchet up pressure for the U.S. to impose sanctions on one of its most important oil suppliers.

The files that have been made public so far have largely confirmed Mr. Chávez's well-known sympathy for the Revolutionary Armed Forces of Colombia, or FARC. But a review by The Wall Street Journal of more than 100 new files from the computers suggests that Venezuela has broader and deeper ties to the FARC than previously known.

These documents indicate Venezuela appears to be making concrete offers to help arm the rebels, possibly with rocket-propelled grenades and ground-to-air missiles. The files suggest that Venezuela offered the FARC the use of one of its ports to receive arms shipments, and that Venezuela raised the prospect of drawing up a joint security plan with the FARC and sought basic training in guerrilla-warfare techniques.

"There is complete agreement in the intelligence community that these documents are what they purport to be," a senior U.S. official said. The Office of the Director of National Intelligence has been sharing its assessments with the White House, this official said.

Washington's stance is likely to hurt Venezuela's already deeply strained relationship with the U.S., its biggest trade partner. It could also add pressure for the U.S. to declare Venezuela a state sponsor of terrorism, alongside Cuba, Iran, North Korea, Sudan and Syria, and impose sanctions.

Mr. Chávez has repeatedly said the files were faked by Colombia. "We don't recognize the validity of any of these documents," Bernardo Álvarez, Venezuela's ambassador to the U.S., said in a Wednesday interview. "They are false, and an attempt to discredit the Venezuelan government."

Interpol, the international police organization, has yet to give its view on the files' legitimacy. Colombia asked Interpol to perform an independent forensic analysis, and next week, Interpol Secretary General Ronald Noble is scheduled to travel to Colombia to present the findings.

Mr. Noble declined to comment on Interpol's conclusions. He said Interpol hasn't yet briefed foreign governments on its findings. "Anyone who has told you that Interpol has informed him about our findings has given you false information," he said.

Cross-Border Raid

The computer files hint at the depth of Mr. Chávez's antipathy towards the U.S., which he often describes as an "empire" oppressing Latin America. According to one document, Venezuela's interior minister, Ramón Rodríguez Chacin, last November asked the FARC to train Venezuela's military in nuts-and-bolts guerrilla tactics -- including "operational tactics, explosives, ... jungle camps, ambushes, logistics, mobility" -- so that soldiers would be prepared to fight a guerrilla war if the U.S. were to invade Venezuela.

The documents are among more than 10,000 files that Colombian intelligence services say came from three computers belonging to Raúl Reyes, the FARC's former second-in-command. Mr. Reyes was killed in March when Colombia's military staged a contentious cross-border raid into Ecuador, where he was camped.

The FARC itself has suggested the files are fake. A FARC statement published on the Web site of Venezuela's Information Ministry ridiculed Colombia's claims about the computer files, saying computers couldn't have survived the Colombian army attack "even if they had been bullet-proof."

A senior staffer in the U.S. Senate, who had been briefed on the contents of the files, cautioned that Mr. Chávez is known for his bombast, and that while tantalizing, the information in the files would need careful corroboration before action is taken against Venezuela. "We need to see proof of what is mentioned in the reports," the staffer said.

There have been some recent indications that the computers contain accurate information. Police in Costa Rica staged a successful raid on a home belonging to alleged FARC sympathizers, and recovered $480,000 in cash, guided by information from the documents suggesting the money would be located there.

In addition, Ecuador's interior minister confirmed that he had met with Mr. Reyes, after an email describing the previously secret meeting was found on the laptops and made public by Colombia.

The FARC, which has been fighting for control of Colombia for nearly a half-century, funds itself mostly through drug trafficking and kidnapping for ransom. The U.S. considers it to be one of the world's main cocaine suppliers.

The FARC is considered a terrorist organization by the U.S., Canada, Colombia and the European Union. For the U.S., any group that deliberately attacks civilians for political reasons merits such a designation. With troop strength estimated at around 9,000 fighters, that would make the FARC Latin America's oldest and largest such group.

However, Colombia's neighbors, including Venezuela, Ecuador and Brazil, don't consider the FARC to be a terrorist organization. Indeed, Mr. Chávez has hailed the group as brother revolutionaries. He has thrown Venezuela's weight behind an effort to remove the FARC from terrorist lists and instead grant the group diplomatic recognition as a "belligerent army."

According to the senior U.S. intelligence official, the Colombian government delivered "thousands" of the controversial documents to Washington in March. Since then, American technical experts have studied them for signs of forgery and to assess whether they correspond to the methods the FARC typically uses to communicate.

"There are no indications whatsoever that they've been fabricated by the Colombians," the official said.

The official said that the most troubling information in the files suggested the FARC's willingness to purchase virtually any type of weapon from any source. The official said Mr. Chávez's government has increasingly been willing to help the FARC reach international buyers. The official cited the FARC's particular desire to acquire surface-to-air missiles, although he said there weren't any signs of the guerrilla movement succeeding.

The FARC Situation

During a speech Wednesday on Latin American relations, President Bush brought up the FARC situation. "Colombia faces a hostile and anti-American neighbor in Venezuela, where the regime has forged an alliance with Cuba, collaborated with FARC terrorists, and provided sanctuary to FARC units."
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According to a study last week from the Senate Foreign Relations Committee, sanctions against Venezuela could backfire if done poorly. The U.S. would need to rally significant regional support or risk that sanctions become "counterproductive" by stirring nationalist or anti-U.S. sentiments.

Venezuela has mounted a vigorous diplomatic offensive to block any move by the U.S. to declare the nation a terrorism sponsor. Such a declaration would prompt U.S. economic sanctions, disrupt $50 billion in annual bilateral trade and jolt the already jittery global oil market, since Venezuela is a major oil producer.

In a speech last month in New York, Mr. Álvarez, Venezuela's ambassador, warned the U.S. would pay a heavy economic price if it made any such move. "There will be very grave economic consequences," Mr. Álvarez said, adding that some 230,000 U.S. manufacturing jobs depend on U.S. exports to Venezuela, which in turn sends some 1.58 million barrels of oil daily to the U.S.

The documents suggest Mr. Chávez is personally involved in helping the guerrillas. In a September 2007 message to the FARC's ruling body, a commander wrote: "Chávez is studying our documents and has said that just like Fidel [Castro] has decided to delegate his other responsibilities to concentrate on the Venezuelan situation, he [Chávez] is ready to do the same to dedicate more time to Colombia."

Colombia has long accused Venezuela of letting the FARC operate on its side of the border, allegations the Venezuelans have denied. But according to one 2005 email, from Jorge Briceño (known as Mono Jojoy, a top FARC military commander), the rebels at that time had some 370 guerrillas and urban sympathizers operating inside Venezuela.

Getting 'Rockets'

One email, apparently sent by a FARC commander known as "Timochenko" to the guerrillas' ruling body in March 2007, describes meetings with Venezuelan naval-intelligence officers who offer the FARC assistance in getting "rockets." The Venezuelans also offer to help a FARC guerrilla travel to the Middle East to learn how to use the rockets.

Colombian military analysts believe the reference is to shoulder-fired antiaircraft missiles, a weapon that the guerrillas desperately need if they hope to blunt Colombia's recent gains. "The FARC realizes that its military problem is air power," says Gen. Oscar Naranjo, who heads the country's national police.

In another email dated early 2007, FARC commander Iván Márquez describes meetings with the Venezuelan military's intelligence chief, Gen. Hugo Carvajal, and another Venezuelan officer to talk about "finances, arms and border policy." Mr. Márquez relates that the Venezuelans will provide the guerrillas some 20 "very powerful bazookas," which Colombian military officials believe is a reference to rocket-propelled grenade launchers.

An officer reached at Gen. Carvajal's office said the general was the only person authorized to comment and he couldn't be reached because he was traveling.

At the meeting with Gen. Carvajal, another Venezuelan general is described as offering the port of Maracaibo to facilitate arms shipments to the guerrillas. The general suggests piggybacking on shipments from Russia -- from which Venezuela itself is buying everything from Kalashnikovs to jet fighters -- to "include some containers destined to the FARC" with various arms for the guerrillas' own use.

A spokesman at the Russian embassy in Washington declined to comment.

The proposals to obtain weaponry are part of a broad program of economic and political support for the FARC from Mr. Chávez's government, some of which was detailed in emails that were made public in the days just after the cross-border military raid that yielded the computer files.

Another email describes a November meeting between two FARC commanders and Mr. Chávez. The commanders, Ricardo Granda and Iván Márquez, report back in the email that Mr. Chávez gave orders to create "rest areas" and hospital zones for the guerrillas to use on the Venezuelan side of the border.

Many documents talk about how to fit generous offers of Venezuelan aid to the FARC's long-term "strategic plan" of taking power in Colombia. In one document dated January 2007, one top FARC commander speaks of a "loan" for $250 million to buy arms which the FARC will pay back once it has reached power. "Don't think of it as a loan, think of it as solidarity," says Mr. Rodríguez Chacin, the interior minister, in another document.

Mr. Rodríguez Chacin's press office didn't respond to a request for comment. Earlier this week, he dismissed Colombian newspaper reports that Interpol had confirmed that the computer documents were authentic, according to an Interior Ministry press release. "Imagine somebody taking [evidence] home and manipulating it as he wants, and afterwards presenting it," he said. "What court in the world will accept that evidence?"

While the documents indicate that the FARC is appreciative of Venezuela's efforts, privately the guerrillas occasionally make fun of the Venezuelans' work habits. "It hasn't been easy for us to adapt to the way of being of the Venezuelans," complains Mr. Reyes in one document. "It doesn't seem as if they are conscious of their boring lack of formality." Mr. Chávez "always leaves things until the last moment."

--David Gauthier-Villars in Paris and David Crawford in Berlin contributed to this article.