The Colombian government is ready to consider a bilateral ceasefire with FARC rebels, even before the end of peace talks, the country's chief negotiator said in an interview released Sunday.

The statement marks a sharp reversal for Colombia, which had previously refused to consider a halt to fighting until the negotiations had succeeded.

"We are willing to accept a ceasefire... provided that it is serious, bilateral, permanent and verifiable," lead negotiator Humberto de la Calle told journalist Juan Gossain, in an interview which was released by Colombia's office of the High Commissioner for Peace.

However, conditions could apply. The Revolutionary Armed Forces of Colombia (FARC) would need to guarantee "that they will assume responsibility in judicial matters and accept national and international verification," de la Calle said.

He added that the negotiations, which have been ongoing in Cuba since 2012, are hardly advancing and are "in their worst moment".

The conflict between the government and FARC guerillas has escalated in recent weeks.

At the end of May, following a month of violence and airstrikes, the FARC lifted a unilateral ceasefire that had been in place for six months.

More than 200,000 people have been killed in Colombia's conflict since FARC was launched in 1964.