Colombia's government and the National Liberation Army (ELN) rebel group have reached a peace deal after months of negotiations, according to both sides.

President Juan Manuel Santos confirmed the 102-day bilateral ceasefire, which will begin on October 1, during a televised speech on Monday.

"The priority is to protect citizens, so during this period, kidnappings, attacks on oil pipelines and other hostilities against the civilian population will cease," he said.

The pact will be renewed as long as progress continues to be made in ongoing negotiations, added Santos.

"Yes, it was possible," the ELN delegation said in a tweet announcing the deal in Ecuador's capital, Quito, which has hosted the latest round of talks since February.

Colombia's biggest rebel force, the FARC, disarmed last month under a peace deal with the government to end more than half a century of civil conflict.

Santos now wants a deal with the left-wing ELN to seal a "complete peace".

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The FARC and ELN formed in 1964 to fight for land rights and protection of poor rural communities.

Despite the Quito-based peace talks, the ELN has refused to stop taking hostages for ransom, launching bomb attacks and extorting foreign oil and mining companies.

"They've attacked [oil] pipelines 43 times since the beginning of the year," Al Jazeera's Alessandro Rampietti, reporting from the Colombian capital, Bogota, said.

Our correspondent said that up to this point the talks in Quito "had been quite uneventful and difficult" on both sides.

"This is definitely the first concrete step forward since those negotiations started six months ago," Rampietti said of the truce.

"The ELN finally has agreed as part of the ceasefire to stop all kidnappings, recruiting miners and attacking the country's infrastructure, in particular, oil pipelines," he added.

"So the expectation is that this ceasefire will bring some relief, in particular to those areas where the ELN has the most influence."

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Monday's agreement was struck in advance of Pope Francis' planned visit to Colombia this week.

"We have said that the visit of Pope Francis should be an extra motivator to accelerate our work for an accord," the ELN said in a statement on its website.

"Once the days of celebration of the presence of Francis have passed, we will continue to insist on advancing toward the de-escalation of the conflict, until complete peace is a reality."

This is the first ceasefire declared by the rebels.