The damaged boat arrives at a Lebanese port
A boat delivering 3.5 tonnes of Cypriot medical aid to the Gaza Strip has been rammed by Israeli naval vessels in international waters, activists say.
The Free Gaza campaign group, which operates the Dignity, also claimed shots were fired towards the crew.
The boat later docked in Lebanon after sustaining serious damage to one side.
Israeli officials confirmed there had been "physical contact" but denied reports of shooting and said the crew had not responded to radio calls.
The 20m (66ft) Dignity was carrying 15 civilian passengers, including several doctors, journalists, a former US congresswoman and a member of the Cypriot parliament, says Free Gaza.
The organisation sent out an urgent statement on Tuesday saying the vessel had been surrounded by at least six Israeli military ships.
Crowds turned out to greet the Dignity as it arrived in Tyre port.
"They are firing live ammunition around the Dignity, and one of the warships has rammed the civilian craft causing an unknown amount of damage," said the statement.
"We heard heavy gunfire in the background before all contact was lost with the Dignity."
The boat was eventually able to reach the Lebanese port of Tyre, where it was greeted by a flotilla of fishing boats.
Heavy damage was clearly visible along one side but there were no reports of any injuries.
The Dignity's captain, Denis Healey, told reporters in Tyre they had been attacked "without any warning, any provocation, or anything".
"There were two other gunboats on our portside with search lights shining at us, distracting us, while a third boat came from ahead and rammed us," he said.
Another crew member, British doctor David Halpin, described hearing "the most almighty three bangs" and said he thought he was going to die.
The boat setting off from Cyprus with aid
A spokesman for the Israeli Foreign Ministry, Yigal Palmor, said the navy had tried to contact the Dignity by radio to say it could not enter Gaza.
Much of the small region has been surrounded by a closed military zone since the Israeli bombardment began four days ago.
"After the boat did not answer the radio, it sharply veered and the two vessels collided, causing only light damage," said Mr Palmor.
Speaking before the ship set sail from Cyprus, spokesperson Renee Boyer said the crew were not taking the voyage lightly and did not expect it to be easy.
Free Gaza said the incident was "an act of terrorism", as well as a violation of international maritime law and the UN Convention on the Law of the Sea.
The group has sent six boat loads of aid into the Gaza Strip in the past few months and said they would try again to deliver the medical supplies.