Colombo- At least 17 people were killed and 69 wounded Tuesday when Tamil rebels fired at a group of civilians fleeing the shrinking area still under rebel control in northern Sri Lanka, the military said.

The civilians were trying to cross the battle lines in the area of Pudukudirippu, 385 kilometres north-east of Colombo, when they were fired upon, military spokesman Brigadier Udaya Nanayakkara said.

He said they were among a group of 970 civilians who were entering the government-controlled area.

The incident came a day after a rebel suicide bomber set off an explosion at a welfare centre where displaced people were crossing into government territory.

At least 20 soldiers and 10 civilians were killed and 64 others, including 40 civilians, were injured in the explosion.

Government troops are fighting in the Mullaitivu district to retake the last strongholds of the separatist rebels. The government accuses the rebels of not allowing civilians there to leave the areas still under guerilla control.

The government has so far received more than 17,000 displaced people during the current offensive in the far north.

The Liberation Tigers of Tamil Eelam (LTTE) have been fighting for more than 25 years for a separate state for the Tamil ethnic minority in the northern and eastern parts of majority-Sinhalese Sri Lanka.

Early last year, the government retook all of the Eastern Province from the LTTE and since then has focused on the north and driven the rebels back to a small patch of land in the north-east.

According to the army, at least 12,000 rebels and 3,5000 soldiers have been killed since the start of the latest campaign in August 2006. (dpa)