Colombo  - Troops were trying Sunday to establish main road access to a rebel-held area in northeastern Sri Lanka and rescue tens of thousands of trapped civilians, military officials said.

They said the manoeuvre was aimed at opening up main road access to an area described as a no-fire zone in the Mullaitivu district.

The military said an estimated 70,000 civilians were trapped, but UN agencies said the figure could be high as 140,000.

Troops by Saturday night were some 800 metres from a bridge on the main road they were trying to secure, the military said.

During the operations to secure the road at least 17 rebels were killed and 22 wounded, the military said.

The fresh move to rescue civilians came after the government rejected a UN call for a pause in military operations to enable civilians to leave, local newspapers reported Sunday.

The call came during meetings between UN Secretary General's Chief of Staff Vijay Nambiar with President Mahinda Rajapaksa and Defence Secretary Gotabhaya Rajapaksa, the Sunday Times said.

Rajapaksa was reported to have said the military operations could not be stopped, the Colombo-based newspaper said.

Troops suspended offensive military operations on April 13 and 14 to coincide with a traditional new year, but rebels had not allowed a mass civilian movement away from the areas held by them, Rajapaksa had pointed out.

The military says they are on the last phase of a long operation to recapture rebel-held areas. It was launched in August 2006, and the rebels and the civilians were now confined to an area of less than 20 square kilometers.

Troops have recaptured vast areas in the eastern and northern provinces of the country since August 2006, while over 65,000 civilians have also been able to escape or were rescued by the International Committee of the Red Cross (ICRC).