The Israeli military on Monday blocked a Malaysian anti-war group's ship from reaching the Hamas-ruled Gaza Strip.
Israel maintains a naval blockade of Gaza and restricts goods transferred overland to the Palestinian territory, citing concerns they could be used to attack Israel.
The military said it ordered the ship to return to an Egyptian port where it had been anchored for several days. But it said the vessel disregarded the order, prompting it to fire warning shots. The ship then changed course to return to Egypt.
The Malaysian group, the Perdana Global Peace Foundation, said its ship was fired at when it tried to reach Gaza. The military denied firing at the ship.
Perdana said no one was injured.
Gaza's prime minister, Ismail Haniyeh, condemned what he called "Israeli piracy" and urged other flotillas to attempt to break the Israeli blockade "so Gaza can have freedom of movement to the outside world."
An aid flotilla is scheduled to depart for Gaza in the third week of June, about a year after Israeli forces raided a similar flotilla and killed nine people on a Turkish boat, the Mavi Marmara.
Israeli military officials have confirmed that preparations are under way to stop any new flotilla.