Colombia's FARC rebels on Friday said they were committed to peace talks with the government, amid rising tensions and renewed clashes in Latin America's longest-running insurgency.

The conflict has flared up this week with four soldiers and five rebels killed in separate clashes, even while the leftist guerrillas and the government resumed peace talks in Havana after a six-day break.

These 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 FARC's lead negotiator, Ivan Marquez, blamed the fighting on the government, saying it had ordered new offensives, prompting the rebels' "legitimate resistance."

"Our insistence is to increase the attempts to achieve peace and to wage a major campaign to protect the dialogue," Marquez said in a statement in Havana as he entered the talks.

He said the government was blocking progress at the peace talks by refusing to consider the FARC's proposals.

"They are numerous and loud, the government's 'NO's' to all our peace initiatives," said Marquez, the second-in-command of the FARC.

He said President Juan Manuel Santos had rejected eight of FARC's proposals, including bringing the talks to Colombia, instead of Cuba, where they are being held.

Santos' administration also refused a bilateral ceasefire agreement that "would allow more dynamic progress" in the negotiations, Marquez said.

The government had rejected the idea of a ceasefire from the start, portraying it as a regrouping tactic and preferring to maintain military pressure on the FARC during the negotiations.

And Thursday, the president said the government will not yield to guerrillas' demands to force a truce "through kidnappings," referring to the abduction of two police officers last week.

The FARC confirmed Wednesday it was holding the men, 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.

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, have an estimated 8,000 fighters.

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