The Israeli navy has seized the Zaytouna-Oliva, a Gaza-bound aid ship, and is currently towing it towards the Israeli port city of Ashdod, according to the initiative's organizers and reports in the Israeli media.
Sondos Ferwana, a media spokeswoman for the International Coalition for the Fourth Freedom Flotilla, told reporters on Wednesday evening that Israeli naval forces had "captured the ship".
The Israeli military, for its part, confirmed the ship's seizure in a statement.
"The Israeli Defense Forces managed to quickly seize the ship without causing any injuries among passengers," the statement read.
According to the military, the crew of the Gaza-bound vessel had initially refused the navy's orders to change course.
"This forced us to intervene and seize the ship before it violated the legal maritime closure imposed on the Gaza Strip," the statement read.
According to reports on Israel's Channel Two television station, the aid ship was intercepted — without resistance — some 80 kilometers off Gaza's coast.
Ferwana, for her part, described the incident as "another act of Israeli piracy", adding that all contact with the ship — which is carrying humanitarian aid and several female activists — had been lost.
"We don't know the fate of the activists aboard," she said.
Passengers on the Zaytouna-Oliva, which set sail from the Spanish city of Barcelona last month, include Irish Nobel Peace Prize laureate Mairead Maguire, Swedish and Algerian lawmakers, a South African Olympic athlete and a Malaysian doctor.
The all-female initiative seeks to break Israel's decade-long blockade of the Gaza Strip and show solidarity with the women of Gaza.
Palestinian resistance movement Hamas, for its part, which has governed the Gaza Strip since 2007, condemned what it described "the Israeli occupation's assault on the aid ship and its intimidation of the activists on board".
In a statement, Hamas spokesman Fawzi Barhoum said the incident amounted to "an act of state terrorism" and another example of Israeli "aggression against the Palestinian people and those who show solidarity with the Palestinian cause".
Barhoum went on to urge the international community to "put an end to Israel's crimes", stressing the need for immediate action "to lift the blockade and rescue the people of Gaza".
In June of last year, Israeli forces intercepted the "Marianne" — which had been taking part in a similar initiative — and arrested all activists on board.
A similar Gaza-bound aid flotilla ended in tragedy in 2010 when the Mavi Marmara, a Turkish aid ship, was raided by Israeli commandos who killed 10 Turkish activists.
Since 2007, the Hamas-run Gaza Strip has groaned under a crippling Israeli/Egyptian blockade that has deprived its almost two million inhabitants of most basic commodities, including food, fuel, medicine and desperately-needed building materials.
In June, UN Secretary-General Ban Ki-moon described the blockade of Gaza as "collective punishment", which, he asserted, "suffocates its people, stifles its economy and impedes reconstruction efforts".