Israel asked the United Nations on Friday to help prevent activists sailing to Gaza on the first anniversary of the bloody Israeli seizure of a Turkish ship that tried to reach the blockaded Palestinian enclave.

Israeli Prime Minister Benjamin Netanyahu's office quoted him telling UN Secretary-General Ban Ki-moon that a mission of around 15 ships expected in late May "was being organised by Islamic extremist elements, among others, with the goal of creating a provocation and bringing about a flare-up".

The Free Gaza Movement, a pro-Palestinian activist umbrella group, said the May flotilla would comprise 15 ships with international passengers including Europeans and Americans.

"We sail not just for Gaza," the group said in a March 31 posting on its Website. "We sail to confront an entire apartheid regime that must be dismantled through citizen action."

Citing security needs, the Israeli navy stopped a six-vessel flotilla in international waters on 31 May 2010 as it tried to reach Gaza, which is governed by the Hamas Islamist group.

Marines killed nine Turkish activists aboard the lead ship, fraying Israel's once-strong ties to Ankara.

Israel has since eased commercial traffic over its land crossings with Gaza, many of whose 1.5 million Palestinians are aid-dependant, but still keeps close control of the sea access.

Rights groups and international aid organanizations had argued that the "eased" blockade has done very to improve Gaza's impoverished population.

Regarding the new sailing, Netanyahu said Israel was "committed to acting firmly against the flotilla," according to the statement. It did not say what the prime minister expected the United Nations to do.

Israel last month caught what it called an Iranian-sponsored shipment of advanced missiles intended for Gaza. Iran denied it.

The United Nations has welcomed measures to relax some trade barriers with Gaza, but wants the blockade, supported by neighbouring Egypt, to be removed entirely.

Gaza was devastated by a 2008-2009 Israeli military campaign killing around 1,400 Palestinians, most of which were civilians, and 13 Israelis. The territory has seen spikes in violence since, with shootings, bulldozings, and combing operations as well as airstrikes on Israel's part. Gazan home-made rockets have also been fired into Israeli territory.

The Free Gaza Movement has called the blockade illegal and flagged persistent Palestinian poverty in the territory. It has championed non-violent political action in a comprehensive challenge to Israel.