Florencia, Colombia ? An American and a Colombian whose bodies were found in the wreckage of a U.S. anti-drug plane were shot to death at close range “in an act of extreme cruelty,” Colombia’s top general said Friday.

The U.S. State Department said three other people in the aircraft, all Americans, might have been taken hostage by the Revolutionary Armed Forces of Colombia, or FARC.

“We have reliable reports that crew members are being held by the terrorist group the FARC,” State Department spokesman Charles Barclay said Friday in Washington. “If these reports are accurate, we demand the crew members be released unharmed immediately.”

The bodies of an American and a Colombian were found in the wreckage of the plane. Gen. Jorge Mora, chief of the Colombian armed forces, told reporters both were “executed, in an act of extreme cruelty.” Both died from the gunshot wounds, said Alonso Velasquez, director of the attorney general’s office in Florencia.

The identities of those aboard haven’t been released.

The single-engine Cessna plane went down Thursday in rebel territory in southern Colombia where the United States has backed a massive campaign in the region to locate and destroy the drug crops with aerial fumigation.

Plantations of coca — the main ingredient of cocaine — are prevalent in this region of humid plains and jungle-covered mountains.

According to one report based on a radio interception, rebels quickly arrived on the scene of the plane crash and captured the survivors.

The State Department said the plane was a U.S. counterdrug aircraft.

The Americans were contractors for the U.S. military’s Southern Command, which oversees military operations in Latin America and the Caribbean, U.S. government officials said in Washington.