Israeli forces seized a Gaza-bound aid boat and detained Greta Thunberg and other activists who were on board early Monday, enforcing a longstanding blockade of the Palestinian territory that has been tightened during the war with Hamas.

The activists had set out to protest Israel's ongoing military campaign in the Gaza Strip, which is among the deadliest and most destructive since World War II, and its restrictions on the entry of humanitarian aid, both of which have put the territory of some 2 million Palestinians at risk of famine.

The Freedom Flotilla Coalition, which had organized the voyage, said the activists were “kidnapped by Israeli forces” while trying to deliver desperately needed aid to the territory.

“The ship was unlawfully boarded, its unarmed civilian crew abducted, and its life-saving cargo — including baby formula, food and medical supplies — confiscated,” it said in a statement.

It said the ship was seized in international waters some 200 kilometers (120 miles) from Gaza.

Israel's Foreign Ministry portrayed the voyage as a public relations stunt, saying in a post on X that "the ‘selfie yacht’ of the ‘celebrities’ is safely making its way to the shores of Israel.”

It said the activists would return to their home countries and the aid would be sent to Gaza through established channels.

It circulated footage of what appeared to be Israeli military personnel handing out sandwiches and water to the activists, who were wearing orange life vests.

Lt. Col. Nadav Shoshani, an Israeli military spokesperson, said the ship was still en route to Israel around midday Monday. It was expected to dock at the port of Ashdod.

Thunberg, a climate campaigner, was among 12 activists aboard the Madleen, which set sail from Sicily a week ago.

Along the way, it had stopped on Thursday to rescue four migrants who had jumped overboard to avoid being detained by the Libyan coast guard.

“I urge all my friends, family and comrades to put pressure on the Swedish government to release me and the others as soon as possible," Thunberg said in a pre-recorded message released after the ship was halted.

Rima Hassan, a French member of the European Parliament who is of Palestinian descent, was also among the volunteers on board.

She has been barred from entering Israel because of her opposition to Israeli policies toward the Palestinians.

She was among six French citizens aboard the boat. French President Emmanuel Macron asked Israel to allow them to return to France as soon as possible, his office said in a statement.

Adalah, a rights group in Israel that said it was representing the activists, said Israel had “no legal authority” to take over the ship because it was in international waters and because it was headed not to Israel but to the “territorial waters of the state of Palestine.”

“The arrest of the unarmed activists, who operated in a civilian manner to provide humanitarian aid, amounts to a serious breach of international law,” Adalah said in a statement.

After a 2½-month total blockade aimed at pressuring Hamas, Israel started allowing some basic aid into Gaza last month, but humanitarian workers and experts have warned of famine unless the blockade is lifted and Israel ends its military offensive.

An attempt last month by Freedom Flotilla to reach Gaza by sea failed after another of the group’s vessels was attacked by two drones while sailing in international waters off Malta, organizers said. The group blamed Israel for the attack, which damaged the front section of the ship.