Pirates have hijacked two more ships off the coast of Somalia, an Iranian cargo vessel, and a Japanese-operated tanker. As Derek Kilner reports from VOA's East Africa bureau in Nairobi, the attacks are the latest in a string of attacks in the busy and dangerous shipping corridor.

The latest attacks, which took place within an hour of each other, follow the hijacking Wednesday of a Malaysian tanker with 39 crew members aboard. Six ships have now been seized by pirates in the Gulf of Aden, between Somalia and Yemen, in the past month.

Andrew Mwangura, of the East Africa Seafarers Assistance Program in Kenya, said the three most recent attacks were likely carried out by the same group of Somali pirates.

"We think this must be the same group because the modus operandi they used is the same," he said. "I think this must be the so-called "Somali Marines". We haven't made any communication, we are waiting to do it later in the evening."

The Japanese Koyo Kaiun-operated tanker Irene (file photo)

An official with the International Maritime Bureau in Kuala Lumpur, Malaysia, Noel Choong, said there were 19 crew members aboard the Japanese ship. The number on the Iranian boat is unknown. Choong said an international naval task force operating in the region had been notified.

The Malaysian ship hijacked on Wednesday is thought to be headed toward the town of Eyl, a base for pirates in the semi-autonomous region of Puntland, in the north of Somalia.

Piracy has long been a major problem in the Gulf of Aden, where a busy shipping corridor connecting the Indian Ocean with the Red Sea, passes by lawless Somalia, which has been without a central government since 1991.

In a potentially lucrative enterprise, pirates regularly seize cargo ships and their crew, demanding ransom payments. Earlier this month, Thai and Nigerian ships were hijacked. A Japanese vessel was seized in July.

The threat of piracy has also complicated the delivery of humanitarian aid to Somalia, where lawlessness and banditry have made overland transport increasingly difficult.

Over one million people have been displaced by a conflict between the struggling provisional government, backed by Ethiopian troops, and Islamist-led insurgents, in what U.N. officials have called Africa's worst humanitarian crisis. 

The U.N. Security Council voted in June to allow international warships to go after pirates operating in Somalia's waters, but there has so far been little increase in the international naval presence.