Colombia's second largest leftist guerrilla group announced Wednesday it is prepared to hold formal peace negotiations with the government aimed at ending a half century old insurgency.

The National Liberation Front, or ELN by its Spanish acronym, would be following in the footsteps of the larger Revolutionary Armed Forces of Colombia, which has been in peace talks with the government for more than two years.

The ELN's leader, Nicolas Rodriguez, alias "Gabino," announced the decision to enter the peace talks in a video posted on the guerrilla group's Twitter account, @ELN_Colombia.

"The government has set forth its willingness to put an end to the armed conflict and to do so has convened the insurgency (to talks)," he said, reading a statement.

"We attend this dialogue to examine the true will of the government and the Colombian state; if we conclude that arms are not necessary, we are prepared to consider whether to stop using them," he said.

The announcement came on the 50th anniversary of the first armed attack by the ELN, which was inspired by the Cuban revolution and is believed to have about 2,500 fighters.

"More than 50 years ago we rose up in arms because we understood that legal paths were closed to the struggles of the people," the ELN leader said. "We still consider that to be the case."

President Juan Manuel Santos on Monday invited the ELN to join his government in formal peace talks, after months of preliminary discussions.

The FARC, meanwhile, has observed a unilateral ceasefire since December 20, which Santos acknowledged on Monday. Santos, however, has so far refused to agree to a truce, arguing that the FARC would use it to regroup.

Those peace talks were nearly derailed by the FARC's capture of a Colombian general on November 16, with Santos suspending the negotiations. But they resumed after General Ruben Dario Alzate was released two weeks later.

"We welcome the new position of the government, which after the capture of General Alzate recognized that confrontation can affect the course of the negotiations," the FARC said in a statement relayed to AFP by its negotiators in Havana.

"The unilateral suspension of the dialogue (over Alzate's capture) put the process in danger," it said.

The Marxist-inspired FARC is the country's largest insurgency with about 8,000 troops.

The conflict, Latin America's longest running leftist insurgency, has killed some 220,000 people and displaced 5.3 million more.