The violence came just days after the government held a lavish ceremony celebrating its recapture of eastern Sri Lanka after 13 years of rebel control there. Military officials have said the Tamil Tigers, which still control parts of northern Sri Lanka, have been trying to launch new attacks in retaliation.

In the deadlier attack, assailants detonated a bomb or land mine along a road Tuesday as a bus carrying soldiers passed by in northern Vavuniya district, bordering rebel-controlled territory, said Lt. Col. Upali Rajapakse, a military spokesman.

The blast tore through the bus, killing 11 soldiers and injuring seven others, a military official said on condition of anonymity because he was not authorized to speak to the media. The blast also wounded eight civilians, including three who were seriously injured and had to be evacuated to the hospital by helicopter, the official said.

Hours earlier, a group of Tamil fighters armed with hand grenades attacked a bunker in the Vavuniya area, killing four village guards, said military spokesman Brig. Prasad Samarasinghe.

Village guards are recruited from ethnic Sinhalese villages bordering rebel areas in northern Sri Lanka to protect their homes against attack.