The Colombian government and the guerrilla group National Liberation Army (ELN) launched Monday their fifth round of peace talks in Ecuador in an attempt to extend a three-month ceasefire that expired today.

The ELN, which has an estimated 1,500 fighters, is the South American country's last active rebel force after the much bigger FARC signed a peace deal with the government in November 2016.

The agreement followed more than five decades of conflict involving left-wing rebel movements, the army and right-wing paramilitary groups, during which about 260,000 people were killed and 7 million displaced.

ELN refused to join a peace process that President Juan Manuel Santos and FARC staged in Cuba between 2012 and 2016. It launched separate talks with the government in February and later agreed to its first ceasefire since it was founded in 1964.

The peace deal and ceasefire have not pacified several parts of the country where criminal and paramilitary groups and FARC dissidents vie for control over the production of coca, the plant cocaine is made from.

Killings of peace campaigners and civil society leaders increased by 45 per cent to 170 deaths last year, the daily El Tiempo reported.

In Monday's talks in Quito, the government was represented by a new chief negotiator, former vice president Gustavo Bell.The negotiations have previously achieved progress in questions such as creating an alert system to protect civil society leaders who have received threats and improving the prison conditions of jailed ELN members.

"We are more than prepared ... to renegotiate the conditions of a new truce," Santos tweeted on Saturday.