Sri Lankan troops repulsed an attempt by Tamil rebels to retake their recently captured stronghold in heavy fighting that killed 21 rebels and three soldiers, the military said Monday. Thirteen rebels and three soldiers were killed in other clashes Sunday in the Mannar, Vavuniya and Welioya regions, bordering the rebels' de facto state in the north, said Brig. Udaya Nanayakkara, the military spokesman was quoted as saying by the Associated Press.