NAIROBI, April 20 (Xinhua) -- Somali pirates are holding three Thai fishing ships and 77 crew members on board off the Somali coast after hijacking the vessels on Sunday, a regional maritime official and EU Naval Force confirmed on Tuesday.

Andrew Mwangura, East Africa Coordinator of Seafarers Assistance Program (SAP) said the pirates hijacked MV Prantalay 11, 12, and 14 with 77 crew members onboard in one of the farthest-off- shore attacks to date.

"The three fishing vessels were hijacked on Sunday and all have 77 Thai crew onboard," Mwangura told Xinhua by telephone from Mombasa.

EU Naval Force Commander John Harbour also confirmed the seizure, saying the three Thai vessels were attacked almost 600 miles (960 km) outside the normal operation area for the EU Naval Force. "These latest hijackings are the furthest east of any pirate attacks in the area since the start of EU NAVFOR's Operation Atalanta in December 2008, almost 600 miles outside the normal EU NAVFOR operating area," Harbour said.

He said the attack so far out at sea was a clear indication that the EU, NATO and CMF were having a marked effect on pirate activity in the area.

Harbour said the MV Prantalay 11 has 26 Thai crew members, MV Prantalay 12 has 25 and MV Prantalay 14 has 26 on board.

He also said the hijacked vessels belong to a Thai based company PT Interfishery Ltd. He confirmed that all 77 Thai crew members were safe and well and that the vessels were heading towards the Somali coast.

Harbour said pirates have expanded their range south and east in response to an increase in patrols by European and U.S. warships off the Somali shore.

Piracy has become rampant off the coast of Africa, especially in the waters near Somalia, which has been without an effective government since 1991.

Ransoms started out in tens of thousands of dollars and have since climbed into millions.

The Horn of Africa nation is at the entrance to the Gulf of Aden, which leads to the Red Sea and the Suez Canal, one of the world's most important shipping channels.About 25,000 ships use the channel south of Yemen, between the Red Sea and the Arabian Sea.