Pirates who seized a Panamanian-flagged chemical tanker carrying 31 crew in waters between India and Somalia demanded a ransom from Tunisian shipping company GMT, a source close to the owner said Friday.

The sum demanded was not immediately known as company manager Farid Abbas could not be reached late Friday.

Tunisian authorities have said they are working to release the tanker while at the same time safeguarding the lives of the crew.

The 24,105-tonne vessel, the Hannibal II, was attacked and boarded by pirates early Thursday while carrying vegetable oils from the Malaysian port of Pasir Gudang to Suez, according to the European Union's anti-piracy mission.

The ship's crew consists of 23 Tunisians, four Filipinos, a Croatian, Georgian, Russian and Moroccan.

Somali pirates are becoming more brazen and keeping ahead of the international naval force seeking to end their high seas marauding, a top UN official said in New York earlier this week.

The pirates have kidnapped almost 100 new crew and passengers from ships in less than a month and there are now at least 438 seafarers and 20 ships held by bandits, according to latest International Maritime Organization figures.

The pirates announced last weekend they had received a record nine-million-dollar ransom for a South Korean supertanker.