Activists trying to bring aid to Gaza today claimed their boat had been rammed by Israeli gunboats in a "criminal attack" in international waters.
The Free Gaza Movement said its vessel, the Dignity, was intercepted by several Israeli vessels as it was heading to the Gaza Strip, which has been under Israeli aerial bombardment since Saturday.
One gunboat rammed the Dignity on the port bow side, causing heavy damage, although no one was hurt, the group said.
"[The Dignity] is taking on water and appears to have engine problems," the movement said on its website. "When attacked, the Dignity was clearly in international waters, 90 miles off the coast of Gaza.
"The gunboats also fired their machine guns into the water in an attempt to stop the mercy ship from getting to Gaza.
"Israel thumbs its nose in the face of maritime law by attacking a human rights boat in international waters and has put all of these human rights observers at risk.
"At no time was the Dignity ever close to Israeli waters. They clearly identified themselves and the Israeli attack was willful and criminal."
The group said the attack took place as the Dignity carried three tonnes of medical supplies at the request of doctors in Gaza.
The crew and passengers were hoping to treat some of those injured in four days of the Israeli air strikes, with hospitals in the territory overwhelmed.
The Dignity is still in international waters, 40 miles off Haifa, and is making its way slowly to Lebanon. The ship flies the flag of Gibraltar, is piloted by an English captain and its passenger list includes Cynthia McKinney, a former US congresswoman.
It left for Gaza from Lanarca in Cyprus yesterday. The group said journalists on board filmed the attack.
An Israeli foreign ministry spokesman, Yigal Palmor, told Reuters there had been no shooting, although two ships made "physical contact".
Palmor said the boat had failed to respond to Israeli naval radio contact and an Israeli vessel "clashed with the ship". He said nobody was hurt and the Israeli ship escorted the aid boat back to Cypriot territorial waters.
Israel declared the coastal territory a closed military zone after it launched air attacks on Hamas targets in Gaza on Saturday in response to Hamas firing rockets into Israel. Israel said the Free Gaza movement boat would not be permitted to dock in the Gaza Strip.
More than 360 Palestinians have been killed in the Israeli attacks. In the same period, four Israelis have died in rocket strikes from Gaza.
The UN relief and works agency, which supports Palestinian refugees and has large programmes in Gaza, said 62 civilians were dead at a conservative estimate.
The overall number of injured is thought to be as high as 1,400 although Gazan hospitals are so overcrowded and short of medicine and equipment that they are turning away all but the most seriously wounded.