BOGOTA, Colombia (AP) _ Leftist rebels said Thursday the government has not honored its promise to remove all troops from an extensive southern region as a condition for holding peace talks.

The impasse over the presence of about 120 soldiers on a base in Caqueta state is the first major snag in peace talks still in the planning stages between the government and the Revolutionary Armed Forces of Colombia, or FARC, the country's most powerful guerrilla group.

Earlier this month, President Andres Pastrana withdrew some 2,000 troops and police from the 16,200-square-mile area as a security guarantee for guerrilla negotiators. He left the 120-member contingent at the base in San Vicente del Caguan, however, insisting they were necessary support staff for the government's negotiating team.

Pastrana says the soldiers are unarmed and would remain on the base.

In its statement to reporters on Thursday in the pullout zone, FARC negotiator Fabian Ramirez said that if Pastrana does not change his mind and remove the troops ``he will bear sole responsibility for the freezing of the dialogues.''

Pastrana responded that he would not back down, and urged the rebels to press ahead with peace talks to end the country's 36-year civil war.

``The government will manage its own headquarters,'' Pastrana told reporters.

Presidential peace envoy Victor G. Ricardo said his preparatory meeting in the southern jungle region with the FARC's top commander, Manuel Marulanda, would go forward as planned on Friday.

The two are to discuss the FARC's insistence that the government exchange 452 jailed rebels for some 300 soldiers and police the rebels have captured over the past year.