Colombia's government suggested Sunday to a leftist rebel group that it declare a Christmas and New Year's truce as a way to free up stalled peace talks.

The National Liberation Army (ELN), smaller than the FARC guerrilla group with whom the government already signed a peace accord, wants until January 10 to consider their next move, government chief negotiator Juan Camilo Restrepo said.

"It would be so good if the ELN used this pause to decree a unilateral ceasefire," Restrepo said in a series of tweets.

The two sides were to have started formal peace talks in late October, but they broke down last month before they could start after the rebels failed to release a hostage, a former congressman named Odin Sanchez.

The ELN is demanding that two imprisoned guerrilla fighters be pardoned.

Restrepo said the two sides would decide January 10 how to move forward.

The ELN declared a unilateral truce in October while Colombians voted in a referendum on a peace accord with the FARC.

The deal was shot down -- critics said it went too easy on the guerrillas -- but was then amended by the government and the FARC, and approved, this second time by Congress.

The FARC and the ELN are the last two leftist guerrilla groups involved in a messy, multi-sided conflict that has killed more than 260,000 people, left seven million displaced and 45,000 more people missing.