(Adds additional rebels killed)

BOGOTA, Nov 18 (Reuters) - Seven Colombian soldiers were killed by landmines and four guerrillas died in a subsequent gun battle over control of a long-time rebel stronghold near the center of the country, the army said on Sunday.

A soldier tripped a landmine that set off a chain of explosions in Tolima province late on Saturday. Those who survived the blasts fired on members of Colombia's biggest rebel force, the FARC, which was born in Tolima in 1964.

Four of the FARC rebels were killed in that exchange.

President Alvaro Uribe has pushed the guerrillas on to the defensive with his U.S.-backed security policies but thousands are still killed every year in this war involving a mosaic of militias funded by the multibillion-dollar cocaine trade.

In a separate weekend battle in the mountain province of Caldas, the army said it killed five guerrillas including a FARC boss suspected of kidnapping a congressman among dozens of hostages Uribe wants to exchange for rebels held in jail.

Leftist President Hugo Chavez of neighboring Venezuela is trying to broker a hostage swap but talks remain in preliminary stages. (Reporting by Hugh Bronstein and Luis Jaime Acosta; editing by Todd Eastham)

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