KUALA LUMPUR, Malaysia - Sea piracy worldwide hit a record high of 142 attacks in the first quarter this year as Somali pirates become more violent and aggressive, a global maritime watchdog said Thursday.

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Nearly 70 percent or 97 of the attacks occurred off the coast of Somalia, up sharply from 35 in the same period last year, the International Maritime Bureau's piracy reporting center in Kuala Lumpur said in a statement.

Attackers seized 18 vessels worldwide, including three big tankers, in the January-March period and captured 344 crew members, it said. Pirates also murdered seven crew members and injured 34 during the quarter.

"Figures for piracy and armed robbery at sea in the past three months are higher than we've ever recorded in the first quarter of any past year," said the bureau's director Pottengal Mukundan.

He said there was a "dramatic increase in the violence and techniques" used by Somali pirates to counter increased patrols by international navies, putting large tankers carrying oil and other flammable chemicals at highest risk to firearm attacks.

Of the 97 vessels attacked off Somalia, he said 37 were tankers including 20 with more than 100,000 deadweight tonnes.

International navies have taken a tougher stance against pirates, with the Indian navy alone arresting 120 mostly Somalian pirates over the past few months. The U.S. and other nations have also prosecuted suspects caught by their militaries, although some were released as countries weigh legal issues and other factors.

Mukundan said the positions of some of the attackers' mother ships were known and called for stronger action to be taken against these mother ships to prevent further hijackings. Pirates held some 28 ships and nearly 600 hostages as of end-March, the bureau said.

Elsewhere, nine attacks were reported off Malaysia and five in Nigeria in the first quarter.