Colombia strengthened its police presence in rebel territory over the weekend after ruling out talks and threatening force to free hostages, including three U.S. defense contractors, held by the insurgents.

Police Capt. Guillermo Solorzano said Sunday that some 150 police officers were sent to the remote southwestern municipalities of Florida and Pradera, where the number of rebels has risen in recent months.

The rebels have demanded the government declare the area a safe haven so the two sides could hold discussions there on swapping jailed rebels for about 60 high-profile hostages.

But President Alvaro Uribe gave up on the possibility of talks with Latin America's oldest and best-armed guerrilla group, the Revolutionary Armed Forces of Colombia, or FARC, after a car bomb on Thursday exploded yards from the country's top army general. He was not hurt but 23 other people were injured.

The FARC has not commented on the explosion.

Uribe now says the only option left for freeing the hostages is military rescue.

"We are going to capture the militias of the FARC that have infiltrated the urban centers of Pradera and Florida and we are going to remove any trace of the FARC from the rural areas," Uribe said Friday in an impassioned speech.

The captives include ex-presidential candidate Ingrid Betancourt and three U.S. defense contractors captured in February 2003 after their small plane crashed into a rebel stronghold during an anti-drug mission.

Uribe's hardened stance drew swift condemnation from Betancourt's mother, who said it condemns the hostages to death. Betancourt was kidnapped in 2002 while campaigning in the jungle.

In the last military operation to rescue hostages, in May 2003, rebels killed 10 hostages, including a former defense minister and provincial governor, as an army rescue squad approached a FARC camp deep in the jungle.

The FARC uses kidnapping to pressure the government and earn money in its fight to establish a Marxist-style state. It has been battling the government for more than four decades. The conflict kills more than 3,000 people each year.