Somali pirates released a chemical tanker yesterday after obtaining a $1.1 million ransom before taking over their next prey, a Japanese ship.

The tanker was called Stolt Valor, Andrew Mwangura, head of the Mombassa-based East Africa Seafarers' Assistance Program, said in a telephone interview today.

Pirate attacks climbed fivefold in the Gulf of Aden in the first nine months of this year as ransom payments spurred raiders to step up their activities, according to the International Maritime Bureau's piracy reporting centre in Kuala Lumpur.

European Union member states on Nov. 10 agreed to send a fleet of warships to the region to combat pirate attacks in the world's most-dangerous seas. The North Atlantic Treaty Organization and at least three other nations have also deployed navy vessels in the region.

A Russian warship stopped an attempted hijacking by Somali pirates of a Saudi ship in the Gulf of Aden, military officials said today, Agence France-Press reported.