There have been least 81 pirates attacks in the region this year, including 32 hijackings, according to the International Maritime Bureau's (IMB) piracy reporting centre in Kuala Lumpur.
Eleven ships and more than 200 crew members are still being held by Somali pirates.
Pirates are well organised in the area where Somalia's northeastern tip juts into the Indian Ocean, preying on a vital maritime route leading to the Suez Canal through which an estimated 30 per cent of the world's oil transits.
Nato warships, along with ships and aircraft from several other nations, have been deployed in the region to protect commercial shipping.
In another development, a Russian warship has joined forces with a British naval force to rebuff a pirate attack on a Danish civilian ship off the coast of Somalia, the Russian navy said on Wednesday.
Russia's Baltic Sea Fleet and the Royal Navy's frigate Cumberland repelled an attack on Denmark's cargo ship in the Gulf of Aden, Igor Dygalo, a Russian navy spokesman, said.
"The pirates tried to shoot at the vessel with automatic weapons and made several attempts to seize it," he said.
"But thanks to the joint efforts of the Russian and British warships the pirates' actions were disrupted."
He said the Russian frigate was now escorting several foreign merchant ships in the piracy-stricken area.
Moscow sent the fleet to the area in September and said at the time its ships would regularly go to zones where pirates were active.
Some observers say the Kremlin is increasingly using the Russian navy to project its renewed power.
The European Union launched on Monday a security operation off the coast of Somalia - its first-ever naval mission - to combat growing acts of piracy and protect ships carrying aid agency deliveries.