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 organized by 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 May 31, 2010 as it tried to reach Gaza.

Marines killed nine Turkish activists in melees 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.

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.

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.