Armed pirates hijacked two ships carrying a total of 50 crew members off the coast of Somalia on Thursday, a maritime official said.
The attacks bring the number of ships seized in the notorious African waters in the past two months to 14 and indicate pirates may be expanding their area of operation, warned Noel Choong of the International Maritime Bureau.
A Greek ship with 25 crew en route to Kenya was captured off Mogadishu, on Somalia's eastern coast. Previously, pirates have largely threatened ships off the country's northern coast, said Choong, who heads the piracy reporting center in Kuala Lumpur.
Four hours later, pirates hijacked the Hong Kong vessel also with 25 crew members in the Gulf of Aden, he said. Suspected pirates in speed boats also chased a Norwegian chemical tanker in the gulf but the ship managed to escape, he said.
A multinational naval force patrolling the area has been informed of the attacks, and ships have been warned to stay clear from Somalia's coast, he said.
"We advise ships to stay at least 250 miles from the coast and even then, they must maintain a strict watch," Choong said. "We urge the U.N. to take serious steps to stop this menace."
Fifty-seven ships, including those seized Thursday, have been attacked off the Somali coast this year, most in the Gulf of Aden. The surge in attacks has prompted the U.S. Naval Central Command to establish a security corridor patrolled by an international coalition of warships.
The Gulf of Aden, which connects the Red Sea and the Indian Ocean, is one of the world's busiest waterways with some 20,000 ships passing through it each year.
Somalia has not had a functioning government since 1991. Pirates there are often trained fighters, many of them dressed in military fatigues and typically armed with automatic weapons, anti-tank rocket launchers and grenades.