Pro-Palestinian activists say 22 boats from a flotilla carrying aid for Gaza have been intercepted by Israeli forces in international waters near the Greek island of Crete.
The organisers of the Global Sumud Flotilla (GSF) denounced the action as "piracy", saying those on board were seized unlawfully more than 965km (600 miles) from Gaza, which is under an Israeli naval blockade.
Israel's foreign ministry said about 175 activists were detained and dismissed the flotilla as a "PR stunt". Foreign Minister Gideon Saar said they would be "disembarked on a Greek beach" later on Thursday.
The GSF's data showed most of the remaining 36 boats in the flotilla were currently close to Crete's south coast.
The flotilla set sail two weeks ago, with a total of 58 vessels joining from Spain, France and Italy, aiming to break Israel's blockade of Gaza.
On Thursday, the GSF said Israeli naval forces had "intercepted, boarded, and systematically disabled and destroyed various boats" in the flotilla during a "violent raid in international waters" north-west of Crete overnight.
"Over 180 civilians from around the world have been directly attacked," it added.
"After detaining participants, smashing an engine and jamming communications, the [Israeli forces] retreated, kidnapping participants or intentionally leaving civilians stranded on powerless, broken vessels directly in the path of a massive approaching storm."
Israel insists its actions comply with international law.
The Israeli foreign ministry said that "due to the large numbers of vessels participating in the flotilla and the risk of escalation, and the need to prevent the breach of a lawful blockade, an early action was required".
"The operation was carried out in international waters peacefully and without any casualties. An initial inspection of the vessels revealed materials that appear to be drugs and contraceptives," it added.
The ministry accused the flotilla's organisers of "joining hands" with the Palestinian armed group Hamas "with the aim of sabotaging President Trump's [Gaza] peace plan transition to its second phase and intended to divert attention from Hamas's refusal to disarm".
Later, it said the flotilla had also actively tried to block an Israeli merchant vessel.
Israel's foreign minister then announced that "in co-ordination with the Greek government, the individuals transferred from the flotilla vessels to the Israeli vessel will be disembarked on a Greek beach in the coming hours".
The Greek Ministry of Foreign Affairs called in a statement for "restraint and universal respect" for international law.
It said Greece had "asked Israel to withdraw its vessels from the region" and offered to receive the passengers and ensure their safe return home.
"The Greek authorities are in consultation with the Israeli authorities regarding the issue of safe disembarkation," it added, and ministry officials are "proceeding to the point of arrival" to coordinate the operation.
A government spokesman earlier told reporters the Israeli naval vessels were outside Greece's territorial waters when the interception happened, and that there was no prior consultation between Israeli and Greek authorities.
"Greek authorities do not have the right to intervene in international waters except in a search and rescue operation. If needed, they are on high alert," Pavlos Marinakis said.
He added that early on Thursday, the Greek coast guard "was informed by its Israeli counterpart that 17 vessels of the flotilla are abandoned and unruly in international waters, and that the people on board are on Israeli warships and are in good health".
Greek centre-left opposition politician Dimitris Mantzos called on the government to explain how it would respond to "this illegal act".
Italian Prime Minister Giorgia Meloni condemned the seizure and demanded Israel immediately release "all the unlawfully detained Italians". Italian media reported that 24 Italians had been detained.
Meloni also called for the "full respect of international law and guarantees on the physical safety of the people on board".
European Union foreign affairs spokesman Anouar El Anouni told reporters: "We reiterate our call on Israeli authorities to respect international law, including international humanitarian law and international maritime law."
Tariq Ra'ouf, a Palestinian-American writer and activist, told BBC News Arabic he was on one of the flotilla's support vessels in Greek waters.
"The spirits on board are high, we are determined to keep doing what we can to support the ending of Israel's illegal siege on Gaza," he said.
"I am feeling shocked and dismayed at the impunity of Israel's actions, and how they have managed to break international law repeatedly but most especially this far away from Gaza."
Israel stopped the previous flotilla set up by the GSF from reaching Gaza last October, arresting and then deporting more than 470 people who were on board, including Swedish climate campaigner Greta Thunberg.
According to the GSF, the latest flotilla's objectives are to "challenge Israel's illegal blockade, advance the opening of a permanent humanitarian corridor, and intensify coordinated international pressure on governments and corporations complicit in its enforcement".
Cogat, the Israeli defence body that controls Gaza's land crossings, said Israel was facilitating the entry of aid into Gaza and that there was "no limit on the amount of aid that can enter".
Earlier this week, a senior UN official warned that the situation in Gaza was steadily worsening, with the territory's 2.1 million population "facing ongoing and deadly Israeli strikes and dire humanitarian conditions".
"While some improvements in access and aid delivery have been observed in recent weeks, unpredictable access, limited operational crossings, and restrictions on critical humanitarian items termed as 'dual use' by Israel continue to constrain UN response," UN Assistant Secretary General Khaled Khiari told the Security Council.
"Food security remains a challenge, while essential services, particularly water, sanitation, and health, are again on the brink of collapse," he added.
Last August, experts from the Integrated Food Security Phase Classification (IPC) confirmed there was a famine in Gaza City.
In December, they said there had been improvements in nutrition and food supplies following a ceasefire agreed by Israel and Hamas in October as part of Trump's Gaza peace plan, but that 100,000 people were still experiencing catastrophic conditions. That figure was projected to decrease to 1,900 by mid-April.
The Gaza war was triggered by the Hamas-led attack on southern Israel on 7 October 2023, when about 1,200 people were killed and 251 others were taken hostage.
Israel responded by launching a military campaign against Hamas in Gaza, during which more than 72,600 people have been killed, including 824 since the start of the ceasefire, according to the territory's Hamas-run health ministry.
