Israeli naval forces on Wednesday intercepted a flotilla carrying aid to Gaza, ending its latest bid to break an Israeli blockade of the war-battered Palestinian territory.

The Global Sumud Flotilla – involving around 45 vessels carrying politicians and activists including Swedish climate campaigner Greta Thunberg – left Spain last month, aiming to break Israel's blockade of the Palestinian territory, where the UN says famine has set in.

Thunberg's ship was among those the Israeli navy intercepted after Israel warned the flotilla against entering the waters it says fall under its blockade, with Israel's foreign ministry posting footage of the 22-year-old retrieving her belongings.

"Around 8:30 pm Gaza time (1730 GMT), several vessels of the Global Sumud Flotilla, including the Alma, Sirius and Adara, were illegally intercepted and boarded by Israeli occupation forces in international waters," the flotilla said.

"Beyond the confirmed interceptions, live streams and communications with several other vessels have been lost," the statement added.

The Israeli foreign ministry posted on X that "several vessels of the... flotilla have been safely stopped and their passengers are being transferred to an Israeli port."

"Greta and her friends are safe and healthy," it added.

Rima Hassan, a French-Palestinian European Parliament member travelling with the flotilla, late on Wednesday on X said that "hundreds" of people "have been illegally arrested and arbitrarily detained by Israel" during the interception.

Hamas, whose October 7, 2023 attack on Israel sparked the war in Gaza, condemned the interception of the flotilla "in international waters" as "crime of piracy and maritime terrorism."

Spain and Italy, which both sent naval escorts, had urged the ships to halt before entering Israel's declared exclusion zone off Gaza, saying their frigates would not pass that mark.

After a 10-day stop in Tunisia, where organisers reported two drone attacks, the flotilla resumed its journey on September 15.

One of its main ships, the Alma, was "aggressively circled by an Israeli warship," the group said, before another vessel, the Sirius, was subjected to "similar harassing manoeuvres."

The flotilla had earlier vowed to press on with its bid to deliver aid to the devastated coastal territory despite what it called "intimidation" tactics by the Israeli military. (AFP)