JERUSALEM — A Gaza Strip-bound aid boat carrying Greta Thunberg and other activists arrived at an Israeli port Monday after Israeli forces stopped and detained them, enforcing a longstanding blockade of the Palestinian territory that has been tightened during the Israel-Hamas war.

The boat, accompanied by Israel’s navy, arrived in Ashdod in the evening, according to Israel’s Foreign Ministry. It published a photo on social media of Thunberg after disembarking.

The 12 activists were undergoing medical checks to ensure they are in good health, the ministry said. They were expected to be held at a detention facility in Ramle before being deported, according to Adalah, a legal rights group representing them.

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

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

“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 about 120 miles from Gaza, and Adalah asserted that Israel had “no legal authority” to take it over.

Israel’s Foreign Ministry portrayed the voyage as a public relations stunt, saying on social media 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 life vests. Israeli officials said the flotilla carried what amounted to less than a truckload of aid.

“This wasn’t humanitarian aid. It’s Instagram activism,” Israeli government spokesperson David Mencer said. “Meanwhile, Israel has delivered over 1,200 truckloads in the last two weeks. So who’s really feeding Gaza and who’s really feeding their own ego? Greta was not bringing aid, she was bringing herself.”

After its 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. About 600 trucks of aid entered daily during the ceasefire that Israel ended in March.

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