Somali pirates who hijacked Saudi oil super-tanker Sirius Star on Thursday demanded a $25 million ransom and set a 10-day deadline amid mounting calls for tougher action on sea bandits.

"We are demanding 25 million dollars 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 told AFP from the ship, now anchored at the Somali pirate lair of Harardhere.

"The Saudis have 10 days to comply, otherwise we will take action that could be disastrous," Said added, without elaborating.

In a sign of growing international frustration over a situation described by the International Maritime Bureau (IBM) as "out of control", Russia announced it would send more warships to combat piracy in the waters around Somalia.

Admiral Vladimir Vysotsky, the top commander of the Russian navy, made the announcement according to a report by RIA Novosti news agency.

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

"This is needed because of the situation that has developed in the vicinity of the Horn of Africa and the Gulf of Aden, where Somali pirates have sharply increased their activities," he was quoted by AFP as saying.

Russia’s ambassador to NATO, Dmitry Rogozin, has meanwhile called for an international ground military operation to better combat rampant piracy in the region.

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

The Somali pirates are estimated to have been paid between $25 million and $30 million in ransoms, the United Nations chief said in his quarterly report to the U.N. Security Council.

Secretary-General Ban Ki-moon also said about 65 merchant ships were hijacked off the coast of Somalia in the first 10 months of the year.

The African Union commission chief, Jean Ping, said the surge in piracy was a result of worsening security in Somalia.

Ping called for "stronger and more coordinated efforts," to return stability to Somalia, "including a rapid deployment of a United Nations peace force", according to a statement released in Addis Ababa.

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

Seized at the weekend in the Indian Ocean some 500 miles (800 kilometers) off the coast of Kenya, the ship became the largest to be taken by Somali pirates and the attack furthest away from Somalia.

The super-tanker was loaded to capacity with two million barrels of oil when it was seized along with its crew of 25 -- 19 from the Philippines, two from Britain, two from Poland, one Croatian and one Saudi.

The Indian 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 late 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 with grapnel hooks tied to rope ladders before neutralizing the crews at gunpoint.

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 centre at the IMB in the Malaysian capital Kuala Lumpur, said "the situation is already out of control".

But the United States, which also has warships patrolling off Somalia, said a military approach was not the answer to a surge of piracy off the Horn of Africa.

"You could have all the navies in the world having all their ships out there, you know, its not going to ever solve this problem," said Pentagon press secretary Geoff Morrell.

The European Union said Tuesday it would launch its anti-piracy operation -- their first-ever -- off Somalia Dec. 8, joining several other warships currently patrolling the region.