* Army veteran being held by FARC rebels
* Jackson said his release was imminent
* Colombian president rejects Jackson's mediation
U.S. civil rights activist Jesse Jackson said on Sunday he will continue to work for the release of a U.S. army veteran kidnapped by Colombian FARC rebels in June, despite the Colombian government's rejection of his mediation.
Jackson, who arrived in Cuba on Friday to talk with Colombian Revolutionary Armed Forces (FARC) commanders who are here for peace talks with the Colombian government, said he was told Afghanistan war veteran Kevin Scott Sutay was free to leave if the logistics were in place to get him out of the jungle.
The FARC had requested on Saturday that Jackson assist with the freeing of Sutay. They say they are holding the former Marine as a prisoner of war and accuse him of being a mercenary.
Also on Saturday, Jackson said Sutay's release was imminent, drawing a quick response on twitter from Colombian President Juan Manuel Santos.
"Only the Red Cross will be authorized to facilitate the handover of the North American kidnapped by the FARC," Santos said in the tweet. "We will not allow a media spectacle."
Jackson retorted on Sunday that the U.S. government supported his efforts and that he hoped the Colombian president "can evaluate the importance of retrieving an American veteran," adding that he still intended to go to Colombia in a matter of days to retrieve Sutay.
The civil rights activist said the Marine's release would draw media attention with or without his mediation.
The FARC kidnapped Sutay as he trekked through jungle in southeastern Colombia despite warnings from the police to abandon the trip through what it said was a "red zone" of guerrilla activity.
Before reaching Colombia, Sutay is thought to have been backpacking through several Central and South American countries.
The FARC appeared ready to release Sutay in July until Santos rejected its initial request that a leftist politician, Piedad Cordoba, oversee the release. It has made no further offer to free him until now.
Jackson appealed to the FARC to release Sutay when he was in Colombia 10 days ago to attend an international conference of Afro-descendent mayors and government officials, saying it would boost the peace talks with the government.
The two sides have been in negotiations hosted by Cuba since last November that aim to end a five-decade conflict that has killed more than 200,000 people.
The FARC began as a communist-inspired peasant army fighting to reduce inequality and redistribute land. Its numbers have been halved in the last decade by a U.S.-backed offensive.
The rebels said in February 2012 that they would stop taking hostages to raise money for their armed struggle, but reserved the right to continue taking prisoners of war.