Colombo - Tamil rebels were intensifying their assault on government troops in what has been described as the last few areas held by rebels in northern Sri Lanka.

An army spokesman said in the latest fighting around the Pudukudirippu area, 390 kilometres north east of the capital Colombo, troops clashed with rebels killing at least seven rebels on Sunday. The bodies along with seven T56 assault rifles were found in the area.

He said several soldiers were injured in the fighting, but did not give further details.

In a related development the United Nations office in Colombo Monday said the rebels had recruited one of its local staff members and three others, including a 16-year-old child.

Another local staff member was being held by rebels after being forcibly recruited two weeks ago.

The army claimed that 15 UN aid workers and their family members have been taken hostage by the rebels and their whereabouts were not known.

On Monday, security forces captured more rebel controlled areas and said they were moving cautiously to regain the last few areas which are being held by the rebels which includes a government declared safe zone meant for civilians.

The government estimates about 65,000 civilians to be present in the area, but UN agencies say the figure is around 150,000.

Military claims the rebels are now confined to an area less than 35 square kilometres.

Some 42,000 civilians have left the rebel controlled areas since beginning of January. The latest batch of about 1,000 people, including 458 children, left the areas on Sunday despite shelling by the rebels, the Defence Ministry said.

Government troops have described the ongoing offensive as the last phase of a long-drawn out military battle which was launched in August 2006 to regain rebel held areas in the north and eastern parts of the country. (dpa)