Sydney – About 260 Sri Lankan asylum-seekers detained in Indonesia have threatened to blow up their wooden boat if the navy forces them to disembark, an Australian report said on Wednesday.

A spokesman told The Australian newspaper that the group, which was stopped en route to Australia, would explode gas canisters and leap into the ocean to avoid being held in Indonesia.

"We have gas canisters and we have told the navy we will blow up the boat and jump into the ocean if they try to force us off the boat," the man, who gave his name as Alex, was quoted as saying.

The boat was stopped off Krakatoa island early on Sunday following a reported direct intervention by Australian Prime Minister Kevin Rudd involving talks with Indonesian President Susilo Bambang Yudhoyono.

Australia's main immigrant detention facilities, on Christmas Island in the Indian Ocean, are under serious strain and have been forced to boost capacity to 1,400 by installing 280 temporary beds in an activity room, an official told AFP.

The explosion threat comes after five asylum-seekers were killed and dozens injured in a blast on a people-smuggling boat stopped off Australia in April. Police have claimed a fire on board was deliberately lit.

Alex told The Australian the ethnic Tamil group was fleeing Sri Lanka's war-torn north, where he alleged widespread atrocities against Tamils in refugee camps.

He said they had each paid 15,000 US dollars to board the wooden boat in Malaysia a fortnight ago after flying there from Jaffna. "We are civilians, not Tamil Tigers," he said, referring to the defeated rebel group.

Indonesia is a key staging point for people-smugglers guiding refugee boats to Australia, where immigration is a major political issue.