Colombo, April 26 Tamil Tiger rebels fighting government forces in north-east Sri Lanka on Sunday evening declared a unilateral ceasefire, following an "unprecedented humanitarian crisis", a BBC report stated on Sunday.

A Tamil Tiger spokesman termed reason behind the move as "unprecedented humanitarian crisis", said the report.

Sri Lanka's defence secretary, however, dismissed the announcement as "a joke", insisting the rebels must surrender.

In a statement, the rebels said they were responding to "calls made by the UN, EU, the governments of India and others".

They said the unilateral ceasefire would come into immediate effect.

The rebels have been beaten back to a 12 sq km (5 sq m) area.

According to the United Nations, some 50,000 civilians remain trapped but the army puts the number at 15,000.

The announcement came as the United Nations' top humanitarian official, John Holmes, was meeting Sri Lankan officials to call for access for aid workers to the war zone and government-run camps for thousands of displaced people.

Aid workers have been barred from the area since the fighting escalated last year.

LTTE says the government is deliberately blocking food aid there - a charge the Sri Lankan authorities have denied.

Defence Secretary Gotabaya Rajapaksa however told the BBC the ceasefire was "a joke" that came from "the losing side." (ANI)