BOGOTA -- Three Colombian leftist rebels accused of kidnapping and murdering three U.S. human rights activists three years ago were captured in a central part of the country, police said.

The Revolutionary Armed Forces of Colombia (FARC) rebels were identified as Orlando Triana, Juan Lopez and Haroldo Buitrago. Judicial police chief Colonel Mario Gutierrez said the three men were arrested Thursday in the villages of Santa Rosa de Viterbo and Cobra, in Boyaca Department, "after a laborios investigation that had been going on for almost four months."

One FARC member is currently in jail for the killings, AFP reported.

Native Americans rights activists Terence Freitas, Ingrid Washinawatok and Lahee'enae gay were kidnapped in February 1999 in northeastern Colombia, where they had been working on environmental and educational projects with the U'wa Indian tribe.

Their bullet-ridden bodies were later found in neighboring Venezuela.

Colombian prosecutors have said the rebels who kidnapped the Americans were in contact with several FARC leaders. They believe the killings were ordered by FARC guerrilla German Briceno with agreement from his brother, Jorge Briceno, the number two in the FARC's military hierarchy.

The rebels admitted in 1999 that the killings had been carried out by its members, but denied they were acting under orders from the FARC leadership.

In April, a federal grand jury in Washington charged six members of the FARC with murder in the 1999 slayings.

Gutierrez said police had witness testimony against the three suspects, who, in his words, had been arrested after careful study of all the evidence.

"I'm not ruling out that the United States will demand the extradition of the rebels," said the police chief, pointing out that if such a request were obtained, it would be carefully examined.

Last month, the U.S. government demanded the extradition of Nelson Vargas, who is accused by Colombian authorities of playing a key role in the abduction and the murder of the activists.

U.S. Secretary of State Colin Powell is to travel to Colombia on Tuesday to show support for President Alvaro Uribe's crackdown on leftist rebels.

Powell will be "reaffirming our commitment to help Colombia combat Narco-terrorism and address Colombia's humanitarian challenges, while helping them to strengthen democratic institutions, protect human rights, foster economic development," State Department deputy spokesman Philip Reeker said.

Powell canceled a planned visit to Colombia last year because of the September 11 terrorist attacks in the United States.

The visit comes as President George W. Bush moves to bolster U.S. assistance to Uribe's administration which is embroiled in battles against two leftist guerrilla groups and is fighting persistent allegations of human rights abuses and support for right-wing paramilitaries as well as the war on drugs.

Bogota is also desperately trying to revive its faltering economy.

The United States has contributed nearly two billion dollars over the past three years to Colombia's anti-drug and counterinsurgency efforts, and will give an additional 300 million dollars in fiscal 2003.