Colombo  - Tamil rebels Tuesday accused Sri Lankan government troops of breaking assurances the army would refrain from using heavy weaponry while an estimated 50,000 civilians remain trapped in the last area held by the rebels.

Both the military and Tamil rebels confirmed that fighting was continuing around the Mullaivikkal area, 390 kilometres north of Colombo, in a narrow coastal strip of about 6 square kilometers in the Mullaitivu district.

The government estimated that 20,000 civilians were trapped in the area, but the UN Office for the Coordination of Humanitarian Affairs said at least 50,000 people remain in the conflict zone.

The Liberation Tigers of Tamil Eelam (LTTE) rebels Tuesday accused the Sri Lanka air force and army of continued use of heavy weapons including airstrikes, despite government assurances that the military would not be using combat aircraft or artillery.

The pro-rebel Tamilnet website said the army Monday night fired cannon shells and used multi-barrel rocket fire, a claim denied by the army, which said the halt of combat operations should not be "misinterpreted" as a ceasefire.

"It is a decision that signals the nearing victory of one of the world's most successful battles against terrorism. It is a decision that displays the genuine will of the Sri Lankan government to rescue its citizens from terrorism," the Defence Ministry said.

International aid was arriving to help some 170,000 civilians who fled the combat zones to government-controlled camps. About 113,000 people fled the area since April 19.

India announced a grant of 20 million dollars while Britain pledged 3.6 million dollars.

United Nations humanitarian chief Sir John Holmes said the UN would immediately release 10 million dollars to the central relief fund, in addition to 10 million dollars authorized last week.

Holmes called for a pause in fighting to conduct a humanitarian assessment of the conflict zone and to deliver in emergency food and medication, a UN statement said.

He also underscored the need for the UN to get full access to the civilians, a demand so far denied by the Sri Lankan government, and the release the 13 UN staff members who have been confined to the camps.

A UN plane carrying relief supplies in Colombo Monday and a second plane is expected on Tuesday.

Military officials say they are on the final phase of crushing the LTTE who have been fighting for an independent homeland for minority Tamils in the north and eastern parts of the country for the last 25 years. (dpa)