(Adds territorial waters detail)

By Stefano Ambrogi

LONDON, June 28 (Reuters) - The world's top maritime body said on Thursday it had asked the U.N. Security Council to help stamp out a growing number of piracy attacks in waters off Somalia.

The International Maritime Organisation (IMO), a U.N. agency based in London, said the alarming rise in attacks in the last few months was putting humanitarian aid shipments at risk as well as maritime commerce.

"The continuing incidence of acts of piracy and armed robbery in waters off the coast of Somalia is of great concern to IMO member states, the IMO secretariat and to me personally," IMO Secretary-General Efthimios Mitropoulos said in a statement.

He said raising the matter at the Security Council should prompt Somalia's transitional federal government to take action.

The IMO said the transitional government may allow foreign navies to pursue the assailants into its territorial waters, which could be key to fighting the problem.

Mitropoulos said that when the IMO last raised the issue of piracy at the United Nations in 2005, attacks and armed robbery off Somalia fell as member states with naval assets and military aircraft operating in the vicinity intervened.

The International Maritime Bureau (IMB), a separate agency that monitors ocean crime and piracy, says there have been 15 ship hijackings and attempted attacks off Somalia this year, most of them since March. That figure compares with ten in the whole of 2006.

IMB Director Pottengal Mukundan told Reuters four ships and their crews were still being held at locations close to Harardheere and Hobyo.

He said a South Korean merchant ship was rumoured to have been hijacked in the last week, but he was still awaiting confirmation of the attack from the ship owners.

Pirates killed a crew member from a Taiwan-flagged merchant ship earlier this month after owners refused to pay a ransom. Somali pirates normally take cargo instead of a life if their demands are not met.

Rampant piracy off Somalia dipped last year during the six-month reign of a militant Islamist group.

Government troops broke its hold over the country with Ethiopian military help in early January, but President Abdullahi Yusuf's interim government is struggling to contain an insurgency in Mogadishu. (For more information about emergency relief visit Reuters AlertNet http://www.alertnet.org email: alertnet@reuters.com; +44 207 542 5791)

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