The Colombian military claims it killed at least 20 members of the Farc rebel group in a bombing raid on one of their camps Saturday, less than two weeks after the rebels unilaterally announced they would observe a two-month cease-fire.

The operation is the largest offensive against the rebels against the Farc since peace talks began in Oslo in October.

While holding a second round of talks in Havana last month, the Farc pledged to cease attacks against the military from Nov. 19 to Jan. 20.

The government refused to participate in the cease-fire, saying it would continue operations against the rebels and would only consider a truce if and when a final agreement is reached during the negotiations.

“President Juan Manuel Santos has always said sustained military pressure against the rebels is key to a successful peace process -- and the weekend's attack provided Farc with a stark reminder of this,” wrote the BBC’s Colombia correspondent Arturo Wallace.

“And with President Santos' popularity at an all-time low and the majority of Colombians claiming to be pessimistic about the prospects of the peace talks, more shows of strength from the government can be expected,” Wallace added.

The government has been skeptical of calls for peace since a previous administrations established a demilitarized zone in rebel territory in 2002, which the Farc used to regroup and plan more attacks against the state.

President Santos has demanded that the Farc disarm within a year and said that the government would provide guarantees that would allow the group to become a legitimate political party.

"This has to be a process of months, rather than years," Santos said, the BBC reported.

Farc has previously rejected any demands to permanently lay down arms. Its numbers have been severely weakened after continued pressure from the military and is currently estimated at around 8,000.

The group has not publicly responded to the military raid on one of its camps. The first stage of negotiations in Havana concluded last Thursday without any substantive results and are expected to resume Wednesday.

The talks are aimed at ending over half a century of armed conflict between the rebels and the state and are meant to specifically address issues of land reform, drug trafficking, political participation and pursuing justice for the victims of the conflict.

According to government estimates, 600,000 people have died since the conflict began in the late 1950s, the BBC reported.

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