BOGOTA (Reuters) - Colombia's Marxist FARC rebels apologized for the "great pain" they caused by kidnapping thousands of people to fund half a century of conflict as the insurgent group prepared to sign a peace accord with the government.

The Revolutionary Armed Forces of Colombia (FARC) said in a video recording late on Sunday that it had taken captives over the years but would not do so again.

The rebels and government are gearing up to sign the accord after reaching agreement on Aug. 24 to end a war that has killed more than 220,000 people and displaced millions. Some 7,000 FARC fighters will be incorporated into society and permitted to form a political party.

"We want to acknowledge, with the sentiment of humanity and reconciliation, that during the conflict the FARC also caused great pain with the retention of people for ransom," FARC's commander and lead negotiator, Ivan Marquez, said in the recording.

"That conduct, while always used to sustain the needs of the rebellion, resulted in harming entire families," he said from Havana, Cuba, where negotiations took place.

Some 27,000 people were kidnapped between 1970 and 2010, according official figures. As many as 90 percent of those were seized by the FARC.

The rebel group amassed a fortune from kidnappings, extortion and the drug trade.

The two sides are scheduled to sign the peace agreement on Sept. 26. The deal will then be put to a vote in a plebiscite on Oct. 2, allowing Colombians to decide whether to accept the accord.

(Reporting by Luis Jaime Acosta; Writing by Helen Murphy)