A group of Somali pirates who have hijacked a tanker loaded with military supplies say they will fight to the death before giving in to Russian and US authorities.

The superpowers have been unable to end the stand-off and remain concerned that the ship's cargo of 33 tanks and other weapons could fall into enemy hands.

But a local official reported that the pirates turned down a demand from Islamist insurgents for some of the arms.

The tense situation off the coast of Somalia began 11 days ago when the pirates took control of the Ukrainian vessel MV Faina.

They have asked for an £11m ransom to release the 21 Ukrainian, Latvian and Russian hostages and the cargo.

"If we are attacked we will defend ourselves until every last one of us dies," Sugule Ali, a spokesman for the pirates, said in an interview over satellite telephone from the ship.

"We only need money and if we are paid, then everything will be OK," he said.