NAIROBI, Kenya (AP) — Four suspected Somali pirates carrying AK-47s and a rocket-propelled grenade seized a bulk carrier with 21 crew on board Wednesday, the fourth ship pirates have seized in less than a week, officials said.

The Panamanian-flagged, Liberian-owned Voc Daisy was taken about 200 miles (300 kilometers) outside the corridor where international warships guard convoys of merchant vessels, said Cmdr. John Harbour, a spokesman for the EU Naval Force.

The hijacking of the Voc Daisy follows an attack on three Thai fishing vessels Sunday. Pirates now hold 15 vessels and 326 crew, according to an Associated Press count.

The Voc Daisy, which had been heading from the United Arab Emirates toward the Suez Canal, was registered with security officials and raised an alarm before the four armed pirates stormed aboard. It was hijacked in the Gulf of Aden about 200 miles (300 kilometers) southeast of Oman.

The vessel has 21 Filipino crew. The latest seizure brings to 45 the number of Filipino sailors in the hands of Somali pirates, Philippine Foreign Affairs spokesman Eduardo Malaya said in Manila.

He said his government was coordinating with the vessel's recruitment agency to determine the condition of the crew.

The hijacking of the three Thai vessels Sunday was almost 600 miles (965 kilometers) outside the normal operation area for the EU Naval Force. Pirates have expanded their range south and east in response to an increase in patrols by European and American warships off the Somali shore.

The International Maritime Bureau said Wednesday that sea attacks worldwide fell by more than a third in the first quarter this year thanks to a decline in pirate raids in the Gulf of Aden.

The number of attacks dipped by 34 percent to 67 in the January to March period, down from 102 incidents in the same period a year ago, the IMB's piracy reporting center in Kuala Lumpur said. Eleven vessels were seized, with 194 crew members taken hostage including 12 who were injured, it said.

The IMB said pirate attacks in the Gulf of Aden dropped to 17 from 41 a year ago, thanks to patrols by international navies and anti-piracy measures by merchant vessels. The east and south coasts of Somalia recorded 18 incidents, down from 21 a year ago.

IMB Director Capt. Pottengal Mukundan said there were cases where international navies in the Indian Ocean have disrupted suspected pirates, destroyed their boats and confiscated equipment.

"Such positive and robust action by the navies against mother ships, pirate skiffs and pirate action groups has been vital to keeping the attacks under control and must be sustained," he added.

Also Wednesday, French officials said pirates mistakenly attacked a French warship off the coast of Somalia, leading the warship to give chase and capture six alleged pirates.

Col. Patrick Steiger said the attackers fired on La Somme, a 3,800-ton refueling ship — but missed. The pre-dawn Tuesday attack far off Somalia's coast was answered by warning shots from La Somme, which then pursued the attackers.

Last year, sea attacks worldwide surged 39 percent to a six-year high of 406 cases, with 49 vessels hijacked.

Analysts blame Somalia's nearly 20 years of lawlessness for fueling piracy's rise. The IMB said the attacks were opportunistic in nature, with pirates sometimes paid multi-million-dollar ransoms.

___

Associated Press reporters Eileen Ng in Kuala Lumpur, Malaysia, and Elaine Ganley in Paris contributed to this report.