The Colombian government and the country's FARC rebels resumed peace talks on Wednesday amid tension over a government offensive on the guerrillas and a deadline set for agreement.

The dialogue restarted in Havana after a five-day recess in which a military offensive by government forces killed at least 20 rebel fighters, leading the leftist guerrilla movement to criticize Bogota for not instituting a ceasefire.

The talks are the fourth attempt to end a conflict that has lasted almost half a century, left 600,000 dead, 15,000 missing and four million displaced in what is Latin America's longest-running insurgency.

The Revolutionary Armed Forces of Colombia formally started talks with Bogota on October 18 in Norway. The negotiations moved to Havana on November 19. Both sides cited progress last week after that round.

But the military's bombing early Saturday of three rebel camps in Narino province, near the border with Ecuador, rattled the calm. The army said 20 rebels were killed.

The government delegation avoided reporters as it headed into the talks, using the back door to go into the convention center where they are being held.

Rebels have called for a ceasefire but the government has refused. It cited its experience in the last talks, for which it created a vast demilitarized zone for the rebels. The government ultimately concluded the guerrillas used that haven to regroup and rearm, and halted those negotiations in 2002. They had started three years earlier.

The rebels are also irritated because President Juan Manuel Santos, although he agreed progress has been made in the first round, warned Sunday that these negotiations have to conclude by November 2013.