The fight on a Turkish ship that was trying to break Israel's blockade of Gaza on May 31 was instigated by "dozens of thugs" who were looking for trouble, Israeli Prime Minister Benjamin Netanyahu said Sunday.

A frame grab from a video released by the Israel Defence Forces shows what the IDF says is an activist hitting Israeli soldiers on a ship heading toward Gaza on May 31. (IDF/Reuters)

The accusation was promptly denied by IHH, the Turkish Islamic charity that organized the ship, and the Free Gaza Movement, which organized the flotilla of which the ship was a part.

Israeli naval commandos boarded the Turkish-flagged Mavi Marmara, leading to the deaths of nine of the activists aboard.

Israel has claimed the commandos were acting in self-defence. The activists on board the flotilla have said they were unarmed except for a few knives and resisted the commandos passively.

Netanyahu and the Israeli government have defended the Israeli action as Turkey and other countries have condemned it.

On Sunday, Netanyahu told a cabinet meeting that "dozens of thugs" from "an extremist, terrorism-supporting" group had set out "to initiate a violent clash with IDF (Israeli Defence Force) soldiers."

They had boarded the ship in a different port from the other passengers and were organized separately, he said.

But IHH head Bulent Yildirim rejected the accusation. All the passengers boarded the ship in the same port, he said.

"Take a look at who was killed. They had pot bellies. They were old. They were young. Who would believe that they received special training?" he said.

Huwaida Arraf, a leader of the Free Gaza Movement, said the passengers had been screened for weapons and that partners in the mission — including IHH — had agreed not to bring weapons.

"Every ship has one or two knives for the captains' use. So on a big ship that holds 1,060 people, certainly knives are not out of the ordinary," she said. She was on another ship in the flotilla, not the Mavi Marmara.

Videos released by the Israeli army show a crowd of men attacking the commandos with clubs and other objects.

UN Secretary General Ban Ki-moon has proposed an international commission to investigate the incident. Israeli officials have said that Netanyahu is open to the idea, but the format proposed needs to be changed.

With files from The Associated Press