Colombia found explosives set to be used in bombs across the capital in reprisal for this week's rescue of leftist rebels' highest-profile hostages, including Ingrid Betancourt, military officials said on Saturday.

The army seized about a tonne of explosives at a farm outside Bogota that it suspected the Revolutionary Armed Forces of Colombia, or FARC, planned to use in attacks over the next few days, said the officials, who asked not to be named.

On Wednesday, the military dealt the rebels the latest in a series of severe blows this year, duping them into handing over French-Colombian politician Betancourt, three American defence contractors and 11 Colombian soldiers and police officers.

The bloodless helicopter rescue in the jungle was hailed around the world but also raised fears that the rebels behind Latin America's oldest insurgency could try to strike back.

This year, the FARC have managed only small-scale attacks in response to setbacks such as the deaths of three senior guerrillas. Last month, four police officers were wounded in a suspected FARC rocket attack in Bogota less than two weeks after the announcement of the death of the group's leader.

The military offensive of President Alvaro Uribe, a U.S. ally, has driven the rebels from urban areas and they now rarely attack the capital - a huge contrast to a decade ago when the cocaine-financed FARC threatened to overrun the government.

This week's rescue could have brought the four-decade-old insurgency to the brink of defeat, political and security analysts said. It deprived the rebels of their biggest bargaining chips, likely hurt morale and exposed their fragmented organization, they said.