Armed Navy ships escorted boats from the Gaza protest flotilla to Ashdod on Monday afternoon, hours after IDF soldiers and activists clashed in a fatal raid.

International activists aboard the ships opened fire on IDF soldiers who boarded the ships to prevent them from breaking the Israeli-imposed sea blockade, the IDF said Monday.

A commando who participated in the raid said that the attack "looked like the Ramallah lynch." IDF said the activists had prepared to kill the soldiers. The soldiers boarded the ships at about 2 a.m. Monday morning after the soldiers called on the ship to stop, or follow them to the Ashdod Port several hours earlier.

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According to IDF reports, at least 15 activists were killed during the ensuing clashes and dozens were wounded. Some of the wounded were evacuated to Israeli hospitals by Air Force helicopters.

Five Navy commandos were also wounded, some of them from gunfire. At least two soldiers were seriously wounded. 

In international reactions, Turkey, Sweden and Greece summonsed their Israeli ambassadors for discussions on the violence.

Palestinian Authority President Mahmoud Abbas also responded to the clashes, which he called a "slaughter," according to an AFP report.

Upon boarding the ships, the soldiers encountered fierce resistance from the passengers who were armed with knives, bats and metal pipes. The soldiers used non-lethal measures to disperse the crowd. The activists, according to an IDF report, succeeded in stealing two handguns from soldiers and opened fire, leading to an escalation in violence.

Al Jazeera on Monday broadcasted footage from the Gaza flotilla's lead vessel, the Mavi Marmara, showing Israeli Navy commandos boarding the ship. Helicopters could also be seen flying overhead.

"It was like a well-planned lynch,” one IDF officer said. “These people were anything but peace activists.”

IDF: Ships will be taken to Ashdod Port

The IDF said that the ships would be taken to the Ashdod Port where, despite the violence, the cargo they hold will be inspected and then transferred to the Gaza Strip via land crossings. Israeli Navy commander Vice-Admiral Eliezer Marom was commanding over the operation from sea.

The Navy made initial contact with the flotilla at 11 p.m. on Sunday ordering the ships to follow them to Ashdod Port or otherwise be boarded.

The actual boarding of the ships took place at 2 a.m. Monday and was yet to be completed by 8 a.m.

Activists aboard the ships repeatedly said they would not respond with violence to the navy's interception of their flotilla prior to the boarding.

Hamas PM condemns 'brutal attack'

Hamas Prime Minister Ismail Haniyeh appeared on Al-Jazeera television to condemn the “brutal attack” and called on the UN to intervene on the activists' behalf.

AP contributed to this report.