The bodies of an American and a Colombian found in the wreckage of a U.S. government plane in Colombia had gunshot wounds, Colombian officials said Friday. President Alvaro Uribe said the two had been murdered.

The single-engine Cessna plane -- carrying four Americans and a Colombian -- went down Thursday in rebel territory in southern Colombia. Three other occupants of the plane are missing and are feared to be in rebel hands.

Rescue crews discovered two bodies in the wreckage and retrieved them.

"There were various bullet impacts on the two bodies," Alonso Velasquez, director of the attorney general's office in Florencia, told The Associated Press.

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

Uribe lamented what he called the deaths of "two people aboard the plane -- a sergeant in our army and an American citizen -- whose murder has been confirmed in the south of the country."

The Colombian president made his comments in a speech inaugurating a hydroelectric plant in western Colombia. He did not elaborate on his statement on the deaths.

It was unclear if the two men had been hit by groundfire while in the plane, or had been shot after the crash.

The Americans were contractors for the U.S. military's Southern Command, which oversees operations in Latin America and the Caribbean, U.S. officials said in Washington. The U.S. Embassy in Bogota said the plane crashed eight minutes before its scheduled arrival in Florencia, a provincial capital.

Colombian troops and U.S. officials continued their desperate search Friday for the survivors. Authorities feared they had been captured by the Revolutionary Armed Forces of Colombia, or FARC, the nation's largest leftist rebel group. DynCorp, a U.S. State Department contractor involved in anti-drug missions in Colombia, said Thursday it was helping in the rescue effort.

Four Colombian soldiers involved in the rescue effort were reported injured by rebel land mines.

"The rebels have a large part of the area mined to stop troops from coming in," said Capt. Lida Zambrano, spokeswoman for the Colombian army's 12th Brigade.

The FARC was also blamed for an explosion Friday in Neiva that blew up a house and killed 15 people, including eight policemen who were investigating a reported rebel plot to assassinate Uribe.

Army troops patrolled the main road near the plane crash site, hoping to intercept the rebels if they tried to move the men out. The army also closed the road between the towns of El Doncello and Puerto Rico -- near where the plane was believed to have crashed -- for several hours late Thursday, local residents said.

The White House said no information was being released about the people on board or their mission out of concern for their safety while the search and rescue efforts continue. "There is a massive effort under way in a very unfriendly part of the country," presidential spokesman Ari Fleischer said.

He declined to comment on whether any of the passengers had been captured since the crash.

The area around the crash site is largely controlled by the FARC. Plantations of coca -- the main ingredient of cocaine -- are prevalent in this region of humid plains and jungle-covered mountains.

The United States has backed a massive campaign to locate and destroy the drug crops with aerial fumigation.

Washington is now moving beyond simply fighting drug trafficking -- which provides profits for rebels and right-wing militias -- to helping the Colombian government directly battle the insurgents.

U.S. special forces in eastern and central Colombia are training Colombian army troops in counterinsurgency tactics and Washington is planning to share intelligence on the rebels with Colombia. Dozens of companies have contracts with the U.S. government to maintain radar stations that track drug flights, fly crop-dusting planes that destroy drug crops and provide other services to Colombian security forces.

Some of the contractors work at the Larandia military base, near Florencia.

The FARC and the National Liberation Army have fought the government for nearly 40 years. About 3,500 people, mostly civilians, die each year in the fighting.