Pro-Palestinian group Freedom Flotilla Coalition (FFC) says Israeli troops have boarded a boat that was trying to bring food aid to the Gaza Strip by sea.
It said the Handala vessel was intercepted in international waters.
Video footage purportedly showed activists on board with their hands up as several armed soldiers took control of the vessel.
The Israeli foreign ministry said the country’s navy stopped the boat “from illegally entering the maritime zone of the coast of Gaza” and breaking the blockade there.
It added that the ship “is safely making its way to the shores of Israel” and that “all passengers are safe”.
In a statement on X, the ministry said that “unauthorised attempts to breach the blockade are dangerous, unlawful, and undermine ongoing humanitarian efforts”.
It did not give any details about where the boat was intercepted.
Meanwhile, the FFC said Handala’s crew of 19 activists and two journalists from various countries – including Australia, France, the UK and the US – had been “kidnapped” by Israeli soldiers.
The group also posted a number of videos with crew members urging people around the world to put pressure on their respective governments to “sanction” Israel.
The boat was carrying baby formula to Gaza, one of the FFC activists said in a post on social media.
In June, a yacht with 12 activists on board – including Sweden’s Greta Thunberg – was intercepted by the Israeli military about 185km (115 miles) west of Gaza.
That expedition, also organised by the FFC, had been aiming to deliver aid to Gaza in defiance of Israel’s blockade and to highlight the humanitarian crisis there.
At the time, the Israeli foreign ministry dismissed it as a “selfie yacht” carrying “less than a single truckload of aid”. It added that the aid transported on the FFC boat, which included baby formula and medicine, would be transferred to Gaza “through real humanitarian channels”.
Israel and Egypt started enforcing a blockade of Gaza when Hamas seized control of Gaza in 2007 by ousting its rivals, a year after winning legislative elections.
Israel stopped all deliveries of humanitarian aid and commercial supplies to Gaza on 2 March and resumed its military offensive two weeks later, collapsing a two-month ceasefire with Hamas.
Israel has since been prioritising aid distribution through the Gaza Humanitarian Foundation, which it backs along with the US.
The UN and other aid groups are refusing to co-operate with the new system, saying it contravenes the humanitarian principles of neutrality, impartiality, and independence.
On Sunday, the Israeli military said it had carried out an airdrop of humanitarian aid to Gaza, following weeks of international pressure and a growing hunger crisis in the Palestinian territory.
Later, the Israel Defense Forces (IDF) said it would open humanitarian corridors for aid convoys in Gaza to allow the UN and other organisations to deliver food and medicine to Palestinians across the strip. The routes will be in place from 06:00 to 23:00 local time (04:00 BST to 21:00 BST).
The IDF also announced what it called a “local tactical pause in military activity” for “humanitarian purposes” in three areas – Al Mawasi, Deir al-Balah and Gaza City – from 10:00 to 20:00 local time (08:00 BST to 18:00 BST) each day until further notice.
Israel launched a military campaign in Gaza in response to the Hamas-led cross-border attack on Israel on 7 October 2023, in which about 1,200 people were killed and 251 others were taken hostage.
At least 59,676 people have been killed in Gaza since then, according to the territory’s Hamas-run health ministry.