Somali pirates hijacked a Greek ship with 28 Ukrainian crew on board in the latest attacks on foreign vessels in the pirate-infested Indian Ocean waters, a regional maritime official confirmed on Saturday.

Andrew Mwangura, the East Africa Coordinator of Seafarers assistance program said the Malta-flagged MV Ariana was seized late Friday but he received the news of the hijacking early Saturday.

"The vessel was hijacked on Friday but we received the reports early on Saturday. The MV Ariana was sailing from Brazil to the Middle East," Mwangura told Xinhua by telephone from the Kenyan port city of Mombasa. "The crew are all Ukrainian and we believe they are safe," Mwangura added.

The incident came hours after a Portuguese warship thwarted an attack on a Norwegian vessel in the Gulf of Aden. The warship, part of a NATO patrol, destroyed explosives they discovered when they captured the pirates.

The explosives can be used for demolition and blasting through walls.

The Portuguese warship, the Corte Real, sent a helicopter to help the oil tanker Kition after a distress call was made. The incident happened about 161 km off the Somali coast.

According to NATO, the Portuguese helicopter chased the pirates back to their "mother ship", or command vessel, and briefly detained about 19 pirates.

Somali pirates have over the past year hijacked dozens of ships and over 250 hostages, and taken millions of dollars in ransom payment. Shipping companies last year handed over about 80 million dollars in ransom payments to Somali pirates.

Insecurity within the Somali waters have pushed up insurance premiums and resulted in high freight costs.

The Horn of Africa nation has been without an effective government since 1991, fuelling the lawlessness which has allowed the pirates to thrive.

Efforts to stop the raiders have had so far only limited success, with international naval patrols struggling to cover the vast areas of the ocean where the gangs operate.

(Xinhua News Agency May 3, 2009)