The French navy seized three boats off Somalia's coast and detained 12 suspected pirates while seizing an arsenal including assault rifles and rocket launchers, the government said Friday.

The operation Thursday by the Floreal surveillance boat was part of the EU anti-piracy mission in the region, the Defense Ministry said in a statement.

Alerted by a Luxembourg maritime surveillance plane on Wednesday, the Floreal was given orders to pursue the suspicious boats. It intercepted the pirate ship and two skiffs about 750 miles east of Hobyo, Somalia, the statement said.

The waters off Somalia, which has been mired by lawlessness since 1991, are teeming with pirates who have hijacked dozens of ships for multimillion-dollar ransoms in the past two years.

The EU runs a maritime anti-piracy mission off Somalia's 1,900-mile-long coast. Together with NATO and U.S. ships, the EU flotilla escorts aid shipments and merchant marines vessels through the Gulf of Aden.

Meanwhile, Swiss authorities reported a separate bandit attack last month off western Africa in which nine crew members were injured.

The Swiss cargo ship Silvretta was boarded and ransacked Oct. 31 off Nigeria's biggest city of Lagos, said Michael Eichmann of the Federal Office for National Economic Supply.

Eichmann described the attack as brutal, saying about 10 pirates had beaten crew members with rifles and broke the captain's fingers while forcing him to open a safe. Almost all of the ship's communications equipment was destroyed, he said, while the pirates robbed mobile phones and other items deemed valuable.

The Silvretta is registered with Switzerland-based company Suisse-Atlantique.