From staff and wire reports

                  BOGOTA, Colombia (CNN) -- A Colombian army helicopter crashed
                  Thursday after being hit by gunfire while providing air support to police
                  officers fighting leftist rebels,

                  An undetermined number of the 22 aboard were killed.

                  Colombian Air Force chief Gen. Hector Fabio Velasco said the U.S.-made Black
                  Hawk helicopter gunship went down in an isolated region of northwest Antioquia
                  as it was flying soldiers into the town of Dabeiba, besieged since Wednesday by
                  a 500-strong column of rebels from the Revolutionary Armed Forces of
                  Colombia, or FARC.

                  "We know that there are victims, there are dead," Velasco told reporters.

                  Velasco confirmed that the U.S.-built Black Hawk helicopter, valued at around
                  $12 million, had been hit by FARC groundfire moments before it crashed.

                  But he insisted the cause of the crash was accidental, saying the rotor on its tail section hit
                  the ground as it was disembarking the soldiers while hovering slightly above the ground in
                  Dabeiba.

                  During the rebels' attack on Dabeiba, one police officer died. Officials said FARC also attacked
                  Bagado, a town in northern Choco state, cutting off communications with a police barracks,
                  staffed by 17 officers, and striking some civilian buildings.

                  "We have no word on their fate," Choco police commander Col. Henry Plaza said of the missing
                  officers.

                  FARC often attacks rural police posts, peppering them with homemade missiles, and either killing
                  the outgunned officers or taking them prisoners.

                  Surge in violence

                  The surge in fighting comes ahead of national elections scheduled for October 29.

                  Black Hawk helicopters are a key weapon in Colombia's arsenal against the
                  guerrillas, and the most expensive component of a recent U.S. aid package to
                  Colombia.

                  However, the crash could spark renewed criticism of the helicopters' use in
                  "Plan Colombia," a joint U.S.-Colombian anti-drug effort.

                  That plan includes a $1.3 billion aid package, which includes U.S. military
                  training and expertise. Under the plan, the United States is to dispatch 90
                  helicopters to Colombia's armed forces.

                  While U.S. service personnel can fly the helicopters, they are not supposed to
                  engage in combat with FARC rebels, who control roughly 40 percent of the
                  country and have ties to Colombia's drug traffickers.

                   CNN Correspondent Marisol Espinosa and The Associated Press contributed to this report.