PARIS - A French frigate captured 11 pirates off the coast of Somalia after foiling an attack on a Liberian-flagged merchant ship, the French defense ministry said on Wednesday.

Naval forces from around the world are battling pirates in the Gulf of Aden, one of the world's busiest shipping routes where even intervention by the U.S. military has not stopped a new spate of hijackings and hostage-taking.

France's Nivose captured the pirates' mothership, which was carrying two small assault boats, 900 km east of Mombasa on Tuesday, the defense ministry said.

The Nivose had started tracking the pirates late on Monday after its helicopter thwarted an attack on the Liberian-flagged Safmarine Asia, a merchant ship.

Supported by a surveillance plane, France's frigate is part of Operation Atalanta, the European Union's anti-piracy mission that also involves German, Spanish, French and Italian forces.

On Sunday, U.S. snipers killed three Somali pirates and freed an American ship captain who had been held hostage for five days.

Last week, French forces attacked pirates holding a yacht with five hostages in a dramatic rescue mission, during which two pirates and one of the hostages was killed.