Colombia's Farc rebels announced a unilateral ceasefire on Monday as it began peace talks in Cuba, but Bogota said it would continue military operations.
Farc negotiator Ivan Marquez said it would halt all acts of sabotage and attacks on government and private property until January 21.
It came as negotiators met for talks in Havana.
Mr Marquez said that the ceasefire was "aimed at strengthening the climate of understanding necessary for the parties to start a dialogue."
But hours later Defence Minister Juan Carlos Pinzon insisted that, while the government hoped the FARC would keep its promise, "history shows that this terrorist organisation has never kept its word."
Former senator Piedad Cordoba, who has served as a go-between with Farc and the government, said the unilateral ceasefire gave Farc "credibility and legitimacy."
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