TEL AVIV, Israel — Israel’s government on Sunday vowed to prevent an aid boat carrying Greta Thunberg and other activists from reaching the Gaza Strip.

Defense Minister Israel Katz said that Israel wouldn’t allow anyone to break its naval blockade of the Palestinian territory, which he said was aimed at preventing Hamas from importing arms.

“To the antisemitic Greta and her fellow Hamas propagandists — I will say this clearly: You should turn back, because you will not make it to Gaza,” he said in a statement.

Thunberg, a climate campaigner, is among 12 activists aboard the Madleen, which is operated by the Freedom Flotilla Coalition. The vessel departed Sicily last Sunday on a mission that aims to break the sea blockade of Gaza and deliver humanitarian aid, while raising awareness over the growing humanitarian crisis 20 months into the Israel-Hamas war.

The activists had said they planned to reach Gaza’s territorial waters as early as Sunday.

Rima Hassan, a French member of the European Parliament who is of Palestinian descent, is among the others onboard. She has been barred from entering Israel because of her opposition to Israeli policies toward the Palestinians.

After a 2½-month total blockade aimed at pressuring Hamas, Israel started allowing some basic aid into Gaza last month, but humanitarian workers 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. The group blamed Israel for the attack, which damaged the front section of the ship.

Israel and Egypt have imposed varying degrees of blockade on Gaza since Hamas seized power from rival Palestinian forces in 2007. Critics of the blockade say it amounts to collective punishment of Gaza’s roughly 2 million Palestinians.

Israel sealed Gaza off from all aid in the early days of the war ignited by the Hamas-led attack on southern Israel on Oct. 7, 2023, but later relented under U.S. pressure. In early March, shortly before Israel ended a ceasefire with Hamas, the country again blocked all imports, including food, fuel and medicine.

Hamas-led militants killed around 1,200 people, mostly civilians, in the Oct. 7 attack and abducted 251 hostages, more than half of whom have since been released in ceasefire agreements or other deals. Hamas is still holding 55 hostages, more than half of them believed to be dead.

Israel’s military campaign has killed more than 54,000 Palestinians, according to the Gaza Health Ministry, which has said women and children make up most of the dead. It doesn’t say whether those killed are civilians or combatants.

The war has destroyed vast areas of Gaza and displaced around 90% of the territory’s population, leaving people there almost completely dependent on international aid.

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