"It is possible to have a peaceful Colombia, a Colombia with no guerrillas, and we will prove that by reason or by force," Santos said in Bogota in his first televised remarks as head of state.

"As long as they don't free the hostages, as long as they perpetrate terrorist acts, as long as they don't return children recruited by force, as long as they keep on planting mines and polluting the Colombian countryside, we will keep on battling those who commit violence, without exception, by any means available," he said.

Earlier in his speech, Santos vowed to "preside over a government of national unity."

"The priority, the obsession of my government, will be to generate prosperity for society through the creation of jobs," he said.

In an early test of Santos' diplomatic skills, his inauguration was attended by the foreign minister of Venezuela, which is at odds with Colombia over accusations that Colombian rebels have found refuge in Venezuela.