Islamist militants in Somalia took steps yesterday to attack pirates behind the world's biggest hijack and rescue the captured Saudi Arabian supertanker, an Islamist spokesman said.

The Sirius Star is carrying $100 million worth of oil and a 25-man crew from the Philippines, Saudi Arabia, Croatia, Poland and Britain.

It is thought to be anchored offshore near Haradheere, about half-way up Somalia's long coastline.

One faction of the Islamists has vowed to attack the gang holding the tanker, in retaliation for them seizing a "Muslim" vessel.

"We have arranged our fighters," Islamist spokesman Abdirahim Isse Adow told Reuters yesterday. "The first step is to cut off pirates inland from those on the Saudi ship by restricting their supplies and cutting their communications."

But the militants - who have been battling Somalia's Western-backed government for nearly two years and have slowly advanced on the capital Mogadishu - are split.

Haradheere residents said another group of Islamists had arrived in the town, apparently with less noble intentions.

"A group of Islamists met some of the pirates here and asked for a share of the ransom," one local man, who gave his name as Farah, told Reuters by telephone.

"The pirates promised them something after the ransom was paid. But there is no deal so far."