Nairobi - Somali pirates on Wednesday hijacked a South Korean cargo ship with 21 crew onboard but failed in an attempt to seize a Greek vessel in the Gulf of Aden, a maritime official said.

"Pirates attacked a fully loaded South Korean bulk carrier en route from Europe to Asia and successfully hijacked her," Noel Choong of the International Maritime Bureau's Piracy Reporting Centre told Deutsche Presse-Agentur dpa.

Piracy has surged this year in the Gulf of Aden, part of an important shipping route from the Indian Ocean to the Mediterranean Sea via the Suez Canal.

The seizure of the South Korean vessel brings the total number of vessels being held by Somali pirates to 11. Over 150 crew members are being held hostage.

Choong said that the attack on the Greek ship was only averted when the IMB called for help after receiving a distress call.

"Earlier in the day, there was an attempted attack on Greek bulk carrier in Gulf of Aden, where a speedboat fired a machine gun on the ship," he said. "We immediately contacted the coalition navy, which sent a warship and a helicopter."

The United Nations Security Council in June approved incursions into Somali waters to combat the pirates and the US Naval Central Command recently set up a security patrol in the area.

However, pirates are still cramming into the Gulf of Aden in search of huge ransoms.

Andrew Mwangura of the Kenya-based East African Seafarers' Assistance Programme said Wednesday that pirates want 1.4 million dollars to release two French sailors.

The pirates also want to secure the release of six of their colleagues arrested by the French navy during an April operation to free the occupants of a luxury yacht.

Mwangura said that while no direct contact had been made with the hostages, they were believed to be in good health.

Somalia's transitional federal government, which has no navy to speak of and is embroiled in combating a bloody insurgency, has been unable to control the pirates

UN agencies say over 6,000 civilians have died in the insurgency that exploded in early 2007 after Ethiopian troops kicked out the Islamist regime and helped reinstate the transitional government.

Almost 1 million Somalis have fled fighting in the capital Mogadishu and are now living in camps outside the city or have crossed the border to neighbouring Kenya.

Somalia has been plagued by chaos and clan-based civil war since dictator Mohamed Siad Barre was toppled in 1991. (dpa)