NAIROBI, Kenya - Striking into the heavily patrolled Gulf of Aden, Somalian pirates seized a British-flagged chemical tanker - the first merchant vessel hijacked there in nearly six months, the same day that a ship was taken by brigands in the Indian Ocean, officials said yesterday.

The double hijacking late Monday shows that, a year after an international naval armada began deploying off Somalia to protect shipping, piracy remains a problem.

The attacks occurred more than 1,000 miles apart, indicating the wide range of territory prowled by pirates and underscoring the difficulty of policing such a large area.

Cmdr. John Harbour, spokesman for the European Union's antipiracy force, said the seizures were probably only a coincidence and not coordinated, because several pirate bands operate in the Indian Ocean and Gulf of Aden.

"Most of the time we are able to disrupt them, but sadly they were successful taking two ships at once," Harbour said. EU officials believe about 1,000 Somalis are involved in the piracy trade.

Somalian pirates have hijacked more than 80 ships in two years, with many of the hijackings earning the pirates multimillion-dollar ransoms.

Resolving the hijacking of the British-flagged tanker could be complicated because the crew comprises nine nationalities, Harbour said.

With the latest hijackings, pirates now hold 12 vessels and 263 crew members, said Noel Choong, who heads the International Maritime Bureau's piracy reporting center in Kuala Lumpur, Malaysia.

A top official from Somalia's weak, U.N.-backed government urged the international community to pursue pirates in their havens on land. "We have reiterated so many times that pursuing pirates on land is crucial to any military response," Information Minister Dahir Gelle said.

The U.K.-flagged tanker St James Park was the first merchant vessel hijacked in the Gulf of Aden in nearly six months, Choong said.

Lt. Cmdr. Corey Barker of the U.S. Fifth Fleet in Bahrain said that the guided-missile cruiser USS Chosin responded to a distress call from the British tanker but that it came after pirates had already taken control of the ship.

The St James Park had set sail from Spain and was headed for Tha Phut, Thailand, Harbour said. It has 26 crew members, from Russia, Georgia, the Philippines, Romania, Bulgaria, Ukraine, Poland, India, and Turkey, he said.

Three hours after the St James Park was hijacked, a Panamanian-flagged carrier with 19 crew members was seized by pirates off the southern coast of Somalia. The ship is managed in Greece.

Greece's Merchant Marine Ministry said the carrier, the Navios Apollon, was carrying fertilizer from the United States to India. It was taken 240 nautical miles northeast of Seychelles, it said. The crew consists of one Greek and 18 Filipinos.