An armed group attacked a Tamil Tiger rebel checkpoint in eastern Sri Lanka on Saturday, killing two guerrillas in what the rebels called a "serious" violation of the country's cease-fire.

The rebels said the attackers retreated toward a government base and accused the army of harboring them.

Military spokesman Brig. Sudhir Samarasinghe called the claim "rubbish" and rejected any suggestion that the military was involved.

A senior Tiger rebel leader known as Karuna left the group in 2004 with about 6,000 fighters. The Tigers accuse the army of using the renegades to attack them, an accusation the military consistently denies.

Saturday's reported fatalities were the first since peace talks last month in Geneva, where the Sri Lankan government and the Tigers agreed to abide by a 2002 cease-fire.

At least 10 rebels were on duty at the checkpoint at the time of the attack near Batticaloa, the violence-wracked main town in eastern Sri Lanka, Tamil spokesman Daya Master said.

"The Liberation Tigers condemn the attack and call upon the Sri Lankan government to stop such provocation," he said.

The rebels began fighting in 1983 for a separate homeland for Sri Lanka's 3.2 million minority Tamils. Norway brokered the cease-fire in 2002, ending a nearly two-decade civil war that had left 65,000 people dead.

Recent violence has killed at least 150 people, including 81 government security officers, and led to an increase in tension and concerns over the stability of the cease-fire.