By JUAN FORERO
 
BOGOTÁ, Colombia, April 9 — Once seen as deferential to civil liberties despite his increasing hold on power, President Hugo Chávez of Venezuela is now coming under sharp criticism from human rights groups that say that torture and excessive force were used to tame recent anti-Chávez protests.

In the latest report, released on Friday in a six-page letter to Mr. Chávez, Human Rights Watch, which is based in New York, accused National Guard troops of using tear gas and electric batons to torture protesters after their arrests.

The letter comes after Venezuela's government lashed out at the Inter-American Human Rights Commission for issuing a voluminous report on what it calls the worsening human rights situation in Venezuela. The commission is an arm of the Organization of American States.

Last week, Jorge Valero, the Venezuelan ambassador to the organization, accused the commission of distorting facts and accused the Bush administration of financing human rights groups as part of a plan to weaken Mr. Chávez. The American representative to the organization, John F. Maisto, fired back in a rare, heated exchange in the organization's headquarters in Washington, accusing Venezuela of undermining the commission.

Mr. Chávez, who is facing opposition efforts to mount a referendum to remove him from office, has denied that his government violated the rights of demonstrators during a week of protests that began on Feb. 27. He has claimed that some of the protesters were armed and violent.

Testimonies collected by Human Rights Watch "suggest a disturbing pattern of conduct that clearly violates international law enforcement standards," José Miguel Vivanco, director of the Americas division for the organization, wrote to Mr. Chávez. Human Rights Watch said the testimonies and documentation that the organization collected were consistent with reports gathered by Venezuelan human rights groups.

Human Rights Watch said 13 people were killed in the protests. It was unclear how many died at the hands of the National Guard and how many were killed by armed protesters. About 400 were arrested.

Human Rights Watch said at least two dozen demonstrators taken into custody were beaten, threatened or tortured by National Guard troops, who tossed tear gas bombs into the police trucks in which they were being held.

"They made us inhale tear gas after closing the canvas sides of the truck and putting on their gas masks," Carlos Eduardo Izcaray, a cellist in the Venezuela Symphony Orchestra who was detained, told Human Rights Watch.

Some of Human Rights Watch's claims are supported by the investigations of two government agencies whose directors are close to Mr. Chávez. The government's human rights ombudsman, Germán Mundarain, reported 7 cases of torture and 17 cases of cruel, inhuman and degrading treatment of detainees. On Wednesday, the attorney general's office said it was investigating allegations of torture against 19 people.