A confrontation at sea between Israeli commandos and pro-Palestinian activists has left at least 10 dead. Israeli forces intercepted an international flotilla that was trying to break a blockade and take hundreds of activists, as well as thousands of tons of humanitarian supplies to the Gaza Strip. The violence has triggered a strong condemnation from Turkey. Military and police forces in Israel remain on alert as Palestinians threaten to protest.

The violence came in the predawn hours of Monday when Israeli forces seized six of the vessels. Activists and Israeli government sources say the interception happened about 60 miles from Israel's coast in international waters.

Video shows pro-Palestinian activists scrambling on board the largest of the ships, a Turkish-flagged vessel, as the Israeli commandos boarded.

Israeli military officials say some of the demonstrators onboard attacked the Israelis with knives and clubs. It also said activists seized a gun from one Israeli soldier and shot at the Israelis.

A military spokesman says troops found revolvers with empty magazines on the bodies of the dead activists.

At a news conference, Deputy Foreign Minister Danny Ayalon said Israeli commandos found weapons on board that he said had been prepared in advance and used against Israeli forces.

"Their method was violent and the results were unfortunately violent," he said. "Israel regrets any loss of life and did everything to avoid this outcome."

The attack happened after Israeli missile boats warned the flotilla, in English, to not approach Gaza which is under blockade by both Israel and Egypt.

A recording of the warning was played on Israeli radio.

Radio Broadcast: "You are approaching an area of hostilities, which is under naval blockade. The Gaza area, coastal region, and Gaza harbor are closed to all maritime traffic. The Israeli government supports delivery of humanitarian supplies to the civilian population in the Gaza strip and invites you to enter the Ashdod port. Delivery of the supplies in accordance with the authorities' regulations will be through the formal land crossings and under your observation after which you can return to your home ports on board the vessels on which you arrived."

Organizers of the flotilla say their intention was primarily to break the blockade, which Israel and Egypt have been enforcing since the Gaza Strip was overrun by the militant Islamist group Hamas three years ago. They rejected allegations that the activists intended to use violent means.

In remarks Monday, the Israeli deputy foreign minister defended Israel's decision to intercept the flotilla.

"The maritime blockade is very legal and justified by the terror that Hamas is applying in Gaza," said Ayalon. "Allowing these ships to go in an illegal way to Gaza would have opened in fact a corridor of smuggling arms and terrorists to Gaza."

Israeli forces sailed the vessels to the Israeli port of Ashdod, where the activists were to be processed and prepared for deportation. Israeli officials say they are prepared to transfer the humanitarian aid aboard the ships after inspecting it.

The vessels are carrying hundreds of activists, and aid that includes medicines, medical equipment, and construction materials.

News of the violence off the coast prompted demonstrations in Gaza. In the West Bank, Palestinian President Mahmoud Abbas called for three days of mourning.

Israeli police have stepped up security throughout the country, but especially around the Arab communities of northern Israel and in Jerusalem.

This is not the first flotilla to try to break the blockade, but previous attempts by activists to enter Gaza have ended without incident.