COLOMBIAN government chief negotiator Humberto de la Calle threw down the gauntlet to the Farc liberation movement yesterday, threatening to abandon peace talks in Cuba.

“The peace process is at its worst moment since we began talks,” he declared.

“I want to tell the Farc in all seriousness that this could end. Someday, it’s probable that they won’t find us around the table in Havana,” said Mr de la Calle, urging the rebels to show more commitment in the talks.

He also said the government would consider a bilateral ceasefire before a final agreement if the rebels accepted judicial responsibility for their attacks and abstained from the drug trade and extortion.

Government rejection of an unconditional bilateral ceasefire and insistence that some Farc members should face trial and imprisonment for military actions have widened a rift between the two sides and cut the chances of a deal.

Optimism had grown over the peace talks, boosted by a Farc agreement to clear landmines in its zones of operation.

Mr De la Calle has been leading the talks with the liberation movement since 2012.

Recent weeks have seen a series of bomb attacks on oil pipelines along rivers, causing a serious environmental disaster that has spread as far away as the Pacific coastline, for which Farc has apologised.

Clashes have grown since a unilateral ceasefire declared by Farc fell apart last month after heightened aggressive activity, especially air strikes, by government forces, in which a number of Farc commanders have been killed.

The Farc leadership in Havana said on Friday, in a conciliatory move, that it was seeking to “de-escalate” the conflict after weeks of attacks in which several soldiers and police were also killed.

Deals have been reached on most of the agenda, with agreements in principle on several issues, including combating drug trafficking, but the process is now under unprecedented strain.

Even if the peace process survives, its biggest obstacle may prove a sceptical public that has to approve any peace deal in a referendum.

“The harsh truth is that Colombians don’t believe in the peace process,” said Mr de la Calle.