MOGADISHU (Reuters) — Somali pirates freed a Saudi supertanker seized in the world's biggest ship hijacking for a $3 million ransom on Friday — but five drowned when their boat capsized as they were making off with their share.

The Sirius Star, carrying 2 million barrels of crude oil worth $100 million, was hijacked Nov. 15 about 420 nautical miles off Somalia.

The Sirius Star is was the largest ship and the furthest from shore of the 43 boats that Somali pirates seized last year, becoming a symbol of their increasing boldness.

Somali pirates have released an Iranian-chartered ship seized in November and said on Saturday they were hopeful a Ukrainian ship loaded with tanks would be freed soon.

Iran's biggest shipping firm said the Delight, a cargo ship ferrying 36,000 tons of wheat to Iran from Germany, was also released on Friday.

Farah Osman, an associate of the pirates speaking to Reuters from Haradheere port near where the tanker was held, said the gang had wanted more money but finally agreed to accept $3 million.

A regional maritime group confirmed the ship's release.

"The last batch of gunmen have disembarked from the Sirius Star. She is now steaming out to safe waters," said Andrew Mwangura of the East African Seafarers Assistance programme, based in the Kenyan port of Mombasa.

Pirates' associate Osman said the gang argued over how to split the ransom money, then at least five were drowned in rough waters that engulfed one of the boats that left the Saudi ship.

"Five of the first eight pirates who took their share of the ransom from the Saudi ship died after their boat capsized," he said.

"Two of them swam and survived. One is still missing. The weather was so terrible that it blew the boat over, then sank it.

"We got five dead bodies and we are still searching for the missing one. The waves were disastrous."

The Sirius Star was captured in November with 25 crew members, 450 miles southeast of Kenya, in the boldest seizure to date by Somali pirates.

There was no immediate comment from Vela International, the Dubai-based shipping arm of Saudi Aramco, which operates the ship.

The Sirius Star was heading south, possibly to anchor off Mombasa for resupplying or to go on to South Africa, Mwangura said. The rampant piracy off Somalia worsened dramatically in 2008 while an Islamist insurgency fuelled chaos onshore.

The piracy in the busy Gulf of Aden and Indian Ocean shipping lanes has sent insurance prices soaring, made some owners choose to go around South Africa instead of through the Suez Canal, and brought an unprecedented deployment of foreign warships to the region.

The crew of the Sirius Star are from Britain, Poland, Croatia, Saudi Arabia and the Philippines.

The US Navy, which has had a warship close to the Sirius Star monitoring the saga, could not immediately confirm its release.

"This is indeed good news that it appears that the ship and the crew of the Sirius Star are to be released," Commodore Tim Lowe, deputy commander of the multinational fleet in the Indian Ocean, said in an e-mailed statement.

"The men who attacked the ship and held the crew hostage are criminals," Lowe said in the statement. "Nearly 300 other merchant mariners are still being held hostage."

The US Navy has said it was planning to launch a force to combat piracy in the Gulf of Aden, an offshoot of an earlier mission.

Chinese warships also began anti-piracy patrols off Somalia this week.

Spain will send up to 395 military personnel and a patrol plane to the waters off Somalia to defend merchant ships from pirates, the government said on Friday.

Underlining the danger, Kenya Ports Authority said on Friday that Somali pirates had attacked a Kenyan fishing vessel north of Mombasa, kidnapping three Indian nationals on board.

Neither the ship nor Kenyan crewmen were taken, officials said, adding that full details of the incident in waters near the Somali border were not available.