The Farc's chief negotiator, Ivan Marquez, has ruled out an extension of the 20 January ceasefire.
Last Friday, two policemen disappeared but Farc chief negotiator Ivan Marquez said he had no knowledge of their whereabouts.
The truce will run from Tuesday until 20 January, negotiator Ivan Marquez said.
Farc lead negotiator Ivan Marquez had said the rebels would halt all attacks from 19 November until 20 January.
During the official launch of the face-to-face negotiations in Norway, Farc delegation head Ivan Marquez renewed calls for a ceasefire.
Intelligence officials said the operation had been ordered by the Farc's number two leader, Ivan Marquez, believed to be in Venezuela.
"We know where Ivan Marquez is, " the president said, saying that the military operation was "a message to him" and to Farc plans to retake parts of Colombia.
On Monday 19 November, Farc lead negotiator Ivan Marquez announced in Cuba that the rebels would halt all attacks from midnight on the same day until 20 January 2013.
Mr Silva said there was evidence a member of the Farc ruling body who goes by the name of Ivan Marquez had been meeting other rebel leaders in Venezuela.
They said that the rebels had been sent by Ivan Marquez, a member of the Farc's seven-man ruling secretariat, and head of the rebels' International Front, which handles the guerrillas' foreign affairs.
While Ivan Marquez complained about a list of "nos" presented by the government, Colombian chief negotiator, Humberto de la Calle, said the violence would not force the government into agreeing a bilateral ceasefire.
President Alvaro Uribe, who has made a relentless war on the Farc the hallmark of his two administrations, sent a message to the rebel leader Ivan Marquez, whom he described as the "diplomat of terror".
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