Aug. 21 (Bloomberg) -- Somali pirates hijacked a Japanese tanker and an Iranian bulk carrier in the Gulf of Aden, the fifth such attack this month, a piracy-monitoring group said.

The vessels were seized last night, Andrew Mwangura, head of the Seafarers Assistance Programme, said in a telephone interview today from Nairobi, the capital of neighboring Kenya. He didn't have information on the names of the ship, the number of crew or their nationality.

``Somali pirates hijacked two more ships last night within hours of each other, an Iranian ship first and later a Japanese ship,'' Mwangura said.

Somalia's 3,300-kilometer (2,060-mile) coastline is considered one of the world's most dangerous stretches of water because of piracy. The number of attacks on vessels more than tripled last year to 31 incidents, compared with 10 a year earlier, according to the International Maritime Bureau. The agency has advised all vessels to stay at least 200 nautical miles (370 kilometers) from the Somali coast.

MISC Bhd., the world's biggest owner of liquefied natural gas tankers, said yesterday one of its ships loaded with palm oil was hijacked off Somalia. The attack occurred a week after a Thoresen Thai Agencies Pcl vessel carrying plywood was seized. A Nigerian ship, the Yenagoa Ocean, was hijacked by Somali militants on Aug. 9, Xinhua reported.

Suez Canal

More than a third of global piracy attacks in the second quarter occurred off Somalia. The country is at the entrance to the Gulf of Aden, which leads to the Red Sea and the 166- kilometer (104-mile) Suez Canal, one of the world's most important shipping lanes.

``The situation is becoming more dangerous'' for merchant shipping sailing through the Gulf of Aden, Noel Choong, head of the International Maritime Bureau, which collates data on pirate attacks, said by phone from Kuala Lumpur today.

The IMB is ``concerned'' about the possibility of ``businessmen'' becoming involved in piracy because of the financial rewards it can offer, Choong said.

``Only the United Nations can solve this problem,'' he said. ``Someone has to take the lead.''

The Japanese and Iranian vessels were taken at about 2 a.m. Greenwich Mean Time today, Choong said, declining to identify either vessel or its cargo for security reasons.

The commodity carrier had a carrying capacity of about 43,000 metric tons, meaning it would be classed as a handymax carrier, while the oil transporter has the capacity to ship about 12,000 tons, Choong said. That means it's probably not the sort of ship used to deliver Middle East crude oil to Europe.

To contact the reporters on this story: Hamsa Omar in Mogadishu via Johannesburg at pmrichardson@bloomberg.net; Alaric Nightingale in London at Anightingal1@bloomberg.net.

Last Updated: August 21, 2008 06:19 EDT