Sri Lanka's military said troops killed 21 Tamil Tiger rebels in gunbattles and mortar barrages in the north of the island on Wednesday, citing intercepts of rebel radio communications.
But the Tigers denied they had suffered any casualties, and said 10 government soldiers were killed and about 50 wounded in a fierce, five-hour battle near the coastal town of Mannar.
Over the past 16 months, Sri Lanka has slipped deeper into a civil war that has claimed more than 68,000 lives since 1983 - including more than 4,000 since late 2005. The intensified violence has left a 2002 ceasefire in tatters.
"Sri Lankan troopers tried to advance into our area and were confronted by our troopers. The Sri Lankan troopers retreated to their original position with heavy casualties," rebel spokesman Rasiah Ilanthiraiyan said by telephone from rebel-controlled territory. "Around 10 were killed in action and around 50 wounded on the government side. Our side has no casualties."