Colombo - Government troops pushed Tuesday into the last few strongholds of the Tamil rebels in north-eastern Sri Lanka, the military said, amid growing concern over civilians caught in the conflict.

Troops were moving in the Mullaitivu district, 395 kilometres north-east of Colombo, after capturing the main town in the area Sunday, military officials said.

Fresh concerns were being expressed both within Sri Lanka and internationally about the plight of civilians in rebel-held areas.

UN Secretary General Ban Ki-moon called on both the government and Tamil rebels to ensure the safety of civilians, including aid workers, and help them move to safe areas. He also called on both sides to respect safe areas and civilian buildings, including schools and medical facilities.

The government has called on the rebels, who have been fighting for autonomy for the minority Tamils in majority-Sinhalese Sri Lanka, to allow civilians to move to a safe zone, but it was unclear if any movement had occurred.

The government estimated that 150,000 civilians are trapped in a 300-square-kilometre area where the fighting is taking place, but aid agencies said the figure was higher and might be around 230,000.

The government until last week was sending food and other aid to civilians in the conflict zone, but the intensified fighting was likely to affect the movement of relief goods, officials and aid agencies said.

Meanwhile, Indian Foreign Minister Pranab Mukherjee was due to visit Sri Lanka for a meeting with President Mahinda Rajapaksa Tuesday night, government sources said.

Mukherjee's visit comes in the wake of concerns expressed by M Karunanidhi - the chief minister of Tamil Nadu, the Indian state that lies across the Palk Strait from Sri Lanka - about civilians in northern Sri Lanka.

Rajapaksa on Sunday called Karunanidhi and Jayalalithaa Jayaram, leader of the Tamil Nadu party All India Anna Dravida Munnetra Kazhagam, to visit the northern part of the country to make a personal appeal to the rebels of the Liberation Tigers of Tamil Eelam to allow civilians to move out of rebel areas.

"We are ready to provide safe corridors for the civilians to go through the army-controlled areas to safer places, but it is now up to the Tamil Tigers to release the civilians," the president told the Asian Tribune in an interview.

Government troops launched military offensives in August 2006 aimed at retaking rebel-held areas and have so far cleared the entire Eastern Province and the north-western and central parts of the Northern Province. Rebels are now confined to a small part in the north-eastern part of the island, according to the government.

The military said it killed more than 12,000 rebels and lost at least 3,500 soldiers in the operations since mid-2006. (dpa)