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 United Nations says famine has set in.

The Israeli navy intercepted the flotilla on Wednesday after warning it against entering waters it says fall under its blockade, with Thunberg's ship among those stopped from going further.

But the flotilla said most of its vessels were continuing their journey as of early Thursday morning, nearing the coast of the Gaza strip despite the interruptions.

"30 boats still sailing strong on their way to Gaza, just 46 nautical miles away, despite the incessant aggressions from the Israeli occupation navy," the flotilla posted on X with a time stamp of 3:20 a.m. local time.

Flotilla spokesman Saif Abukeshek said Israeli forces had intercepted 13 boats carrying around 200 people in total, including many from Spain and Italy.

But, he said in a video posted on Instagram, "our mission is going on".

"They are determined. They are motivated, and they are doing everything within their hands to be able to break the siege by this early morning," he said of the remaining vessels.

The interceptions occurred at about 8:30 pm on Wednesday, the flotilla said, describing the move as "illegal" as they were traversing international waters.

"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".

It posted footage of the 22-year-old Thunberg retrieving her belongings, adding: "Greta and her friends are safe and healthy."

Hamas, whose Oct. 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 organizers reported two drone attacks, the flotilla resumed its journey on Sept. 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 maneuvers".

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.

It said on X it remained "vigilant as we enter the area where the previous flotillas were intercepted and/or attacked".

In Italy, which has already seen a general strike in support of the flotilla, hundreds turned out late on Wednesday in Rome in its support.

Pro-Palestinian demonstrators in Naples blocked trains at the southern Italian city's main station for around an hour before being cleared by police.

Unions have called for another strike on Friday to urge stronger action from the government against Israel's actions.

Colombian President Gustavo Petro said he will expel all remaining Israeli diplomats in the country over the interception.

Turkey's foreign minister called it "an act of terrorism that constitutes the most serious violation of international law and endangers the lives of innocent civilians".

Israel blocked similar attempts in June and July.

Spain's digital transformation minister, Oscar Lopez, had urged the flotilla not to cross into Israel's declared exclusion zone, extending 150 nautical miles off Gaza.

Italy, too, urged the activists to "stop now" after its frigate halted at the that limit.

The activists said Spain and Italy's decision was an attempt to "sabotage" their endeavors.

Spanish Prime Minister Pedro Sanchez said the activists posed no threat and urged Israeli counterpart Benjamin Netanyahu not to consider them one either.

And Italy's Giorgia Meloni said the voyage could jeopardize US President Donald Trump's latest proposed Gaza peace plan, currently still under negotiation.