MOGADISHU -- Somali pirates who hijacked a Saudi oil super-tanker demanded a $25-million ransom Thursday amid calls for tougher action to end threats to one of the world's key maritime routes.

As global frustration built and a major shipping company ordered some of its vessels to avoid the Gulf of Aden, the pirates set a 10-day deadline for the ransom payment.

"We are demanding $25 million (€20 million) from the Saudi owners of the tanker. We do not want long-term discussions to resolve the matter," a pirate who identified himself as Mohamed Said said from the ship.

"The Saudis have 10 days to comply, otherwise we will take action that could be disastrous," Said told AFP from the ship now anchored at the Somali pirate lair of Harardhere, without elaborating.

Seized at the weekend in the Indian Ocean some 500 miles (800 kilometers) off the coast of Kenya, the Sirius Star tanker was loaded to capacity with two million barrels of oil and the biggest vessel to be seized by pirates so far.

After the International Maritime Bureau (IMB) described the situation as "out of control," Arab Red Sea states meeting in Cairo Thursday pledged cooperation to end the threat -- but offered few specifics.

Russia announced it would send more warships to combat piracy in the treacherous waters.

Admiral Vladimir Vysotsky, the top commander of the Russian navy, said: "After the Neustrashimy (Fearless), ships from other fleets of the Russian navy will head to the region," referring to a frigate sent to the area in September.

Russia's ambassador to NATO, Dmitry Rogozin, meanwhile called for an international ground military operation in the region to crush piracy, to boost sea patrols that are yielding thin results.

"It's up to the European Union, NATO and others to launch a coastal land operation to eliminate the pirates," Rogozin told AFP, insisting that "naval action alone will not be enough to liquidate the threat of piracy".

British Foreign Secretary David Miliband urged the world to firmly fight the "scourge of hostage taking."

In a sign of the havoc being wreaked by the pirates, one of the world's largest shipping companies, Danish group A.P. Moller-Maersk, ordered some of its vessels to avoid the Gulf of Aden.

"Vessels without adequate speed or freeboard will for the time being avoid the Gulf of Aden and seek alternative routing south of the Cape of Good Hope and east of Madagascar," the company said.

Somali Prime Minister Nur Hassan Hussein warned that piracy will rage unless the world helps restore a functional government in Somalia, which collapsed after the 1991 ouster of dictator Mohamed Siad Barre.

"The problems of pirates will only be resolved when the international community helps Somalia to stand on her feet," Hussein told reporters in Mogadishu.

Saudi Arabia's foreign minister, Prince Saud al-Faisal said on Wednesday that the super-tanker's owners are in talks with the pirates, but the company that operates the vessel has remained tight-lipped about the claims of negotiations.

At the Cairo talks, foreign ministry spokesman Hossam Zaki said Egypt would consider all possibilities. Egypt's economy heavily relies on revenue from tourism and maritime traffic through the Suez Canal, which links the Mediterranean Sea to the Red Sea.

The Indian stealth frigate INS Tabar, one of dozens of warships from several countries protecting commercial shipping lanes in the Gulf of Aden, sank a Somali pirate ship Tuesday after coming under fire, navy spokesman Nirad Sinha said.

Pirates use mother ships, generally hijacked trawlers or deep-sea dhows, to tow speedboats from which they launch their attacks.

The incident came as shipping groups reported a new surge in hijackings off Somalia, with three captured since the Sirius Star was taken.

Noel Choong, head of the piracy reporting center at the IMB in the Malaysian capital Kuala Lumpur, said "the situation is already out of control," but praised the Indian navy for striking the mother ship.

"We hope more navies will follow suit and stop suspected pirate boats," he added.

Choong however said that destroying pirate ships or confiscating equipment "is not the whole answer, as it is not a deterrent... it is just to disrupt their operations. What is needed is firm action and a firm deterrent ..."