At least 20 Farc rebels have been killed in Colombia after the military launched bombing strikes on one of their camps, the army says.It is said to be the biggest military operation against the group since peace talks began in Oslo in October. The camps were in Narino province near the Ecuadorian border, commander Gen Leonardo Barrero told AFP news agency.The strike comes as President Juan Manuel Santos said the rebels had less than a year to abandon their weapons. Mr Santos said the government would offer all necessary guarantees so the Farc could disarm and join the political process."This has to be a process of months, rather than years,” he said.Mr Santos said any attempts to delay disarming were unacceptable. The Farc has not responded to Mr Santos’ deadline.He made his comments after the rebel group acknowledged that it was holding what it called "prisoners of war”, contradicting its previous denials.In February, the rebels announced that they would stop all political abductions and kidnappings for ransom. But victims’ groups say the kidnappings have continued and not all hostages have been released. The peace talks between the Colombian and the Farc began in Norway on 18 October before moving to Cuba’s capital, Havana, a month later. The first stage of the dialogue aimed at ending five decades of conflict ended last Thursday. The talks are due to resume on Wednesday.All previous attempts to reach a deal have failed.The government ended the last peace talks in 2002, accusing the rebels of trying to regroup in a demilitarised zone.According to government estimates, 600,000 people have died since the conflict began in Colombia, with millions more displaced.