Colombia's armed conflict flared up again Thursday, leaving four soldiers and five rebels dead in separate clashes as the government and leftist rebels resumed peace talks in Cuba.

They were the first combat casualties for the Colombian military since the Revolutionary Armed Forces of Colombia ended a two-month unilateral ceasefire on January 20.

The military said four of its soldiers were killed and two wounded early Thursday when they tried to bloc FARC rebels from entering the town of Policarpa in southern Narino province.

In the northwestern province of Antioquia, meanwhile, five guerrillas were also killed during an army operation in the town of Nudo Paramillo, an army spokesman said.

The fighting broke out on the same day that peace negotiations aimed at ending Latin America's oldest insurgency resumed in Havana between representatives of the government and the FARC after a six-day break.

The latest round of talks comes amid rising tensions.

Besides Thursday's clashes, FARC rebels also have kidnapped two policemen and bombed a section of an oil pipeline in southern Putumayo province.

The FARC confirmed Wednesday it was holding the two police officers, calling them "prisoners of war" and drawing a distinction between the capture of security forces and kidnappings for ransom, which it has pledged to stop.

The abductions were the first by the FARC since April 2012 when the group freed 10 police and soldiers who had been in captivity for years.

Humberto de la Calle, the chief government negotiator, said Wednesday that the kidnappings were "a mistaken response that constitute an attack on the (peace) process."

He said the rebels would use the policemen's abductions to try to press for a ceasefire by both sides.

"We are not going to accept pressures to agree to a ceasefire," he said.

The rebel group's delegation in Havana, meanwhile, denied having any information about the two captive police officers, and reaffirmed their willingness to continue peace talks with the government of Juan Manuel Santos.

"So far, we have no official report related to (the kidnapping) or about whether or not it was carried out by the FARC," chief negotiator Ivan Marquez said Thursday, moments before resuming negotiations.

Asked if the policemen would be released, Marquez, who is the rebel group's number two official, said: "We have to wait to see what the position is of whatever bloc or group that has undertaken that action."

Marquez said the FARC was committed to peace talks "until we find a path that leads us to peace."

The talks, which began in November, are the first in a decade. Three previous attempts at a negotiated end to the conflict failed.

The FARC, formed in 1964, has an estimated 8,000 fighters engaged in Latin America's oldest insurgency.

The government delegation, headed by former Colombian vice president Humberto de la Calle, made no statement when it arrived Thursday at the convention center in Havana, where the talks have been held since they began November 19.