The Colombian government and the country's second-largest rebel group said Thursday they were launching a formal peace process.

Colombia's peace envoy and the head of the National Liberation Army, or ELN, said they had agreed to create a political environment for peace and to include non-governmental members of Colombian society in formal talks.

Both sides presented proposals for topics to be discussed in the next phase, but did not give specifics.

Government representative Luis Carlos Restrepo and ELN military chief Antonio Garcia met behind closed doors with representatives of other countries helping mediate the peace process after delivering their brief announcement to reporters.

The ELN, the country's second-largest rebel group after the Revolutionary Armed Forces of Colombia, or FARC, has been fighting its government since the 1960s for social changes. It has seen its forces dwindle to fewer than 3,500 fighters, however, after a military offensive by Colombian President Alvaro Uribe.

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Meeting in Havana as a neutral location in recent days, the government, rebel representatives and members of civil society have discussed possible compromises to de-mine rural areas, stop displacement of Colombians caused by violence and release rebel prisoners — a top ELN demand.

Those compromises could ease the intensity of the armed conflict that has been ripping apart the South American country for more than four decades.

Colombia's talks with the ELN in Cuba came after Uribe withdrew his offer to negotiate a humanitarian prisoner exchange with the FARC following a car blast at the military university in Bogota blamed on that larger group.

Restrepo had said earlier this week that the government's talks with the ELN would not be harmed by the violence blamed on the FARC.