The Israeli navy has intercepted boats carrying aid to Gaza and detained the activists aboard, including Swedish climate campaigner Greta Thunberg.

Israel’s Foreign Ministry said several vessels that form part of the Global Sumud Flotilla (GSF) had been “safely stopped” and that those aboard were being transferred to an Israeli port.

It added the navy had told the vessels to change course as they were “approaching an active combat zone”.

The GSF has said boats are still being intercepted on Thursday morning. Earlier, it said 30 boats were still “sailing strong to Gaza” and were 46 nautical miles from their intended destination.

They described the interception as “illegal” and “not an act of defence” but “a brazen act of desperation”.

The group has alleged that one vessel within the flotilla was “deliberately rammed at sea” and said additional boats were hit by water cannons.

“It clearly reveals the extreme lengths to which the occupier will go to ensure Gaza remains starved and isolated,” GSF wrote on social media.

“They will attack a peaceful civilian mission because the success of humanitarian aid means the failure of their siege.”

The Israeli Foreign Ministry said the flotilla had been informed it was “violating a lawful naval blockade” that covers the waters next to Gaza – though it is unclear if the boats had entered the blockade zone.

It posted footage from the interception showing Thunberg sitting on the deck of a boat, being handed water and a jacket by a member of the Israeli military.

Later on Thursday, the foreign ministry said detained activists were being taken to Israel before procedures begin to deport them to Europe.

Livestreams from the boats suggest not all of the 44 vessels have been boarded and evacuated.

The Israeli government, which has branded the GSF’s attempt to transport humanitarian aid to war-torn Gaza as “provocation”, said: “Greta and her friends are safe and healthy.

The GSF said multiple ships including the Alma, one of the main vessels, as well as the Surius and the Adara, had been intercepted and boarded.

Prior to that, it accused the Israeli military of “intentionally damaging ship communications, in an attempt to block distress signals and stop the livestream of their illegal boat boarding”.

It said the flotilla had been 70 nautical miles from Gaza’s shoreline when the intervention had occurred. The group had hoped its vessels would arrive in Gaza on Thursday morning.

People have gathered in Greece, Italy, Germany, Tunisia and Turkey to protest against Israel’s interception of the flotilla.

In a statement the UN High Commissioner for Human Rights, Volker Türk, called for Israel to “urgently lift the blockade on Gaza and allow the entry of life-saving material through all means possible”, adding it must agree to facilitate impartial humanitarian relief schemes “without hindrance”.

Italian unions have also called a general strike on Friday in “defense of the flotilla, constitutional values, and for Gaza”.

Turkey’s foreign ministry condemned the interception as an “act of terrorism”, and called for the “perpetrators of this attack” to be held accountable.

Colombian President Gustavo Petro has expelled all remaining Israeli diplomats from the country in response, and denounced the interception as an “international crime by Netanyahu”.

Petro also terminated Colombia’s free trade agreement with Israel, which has been in place since 2020, and called for the release of two Colombians who were aboard the flotilla.

Irish Deputy Prime Minister Simon Harris called the reports “concerning” and said he expects Israel to uphold international law, with at least seven Irish citizens among the detained, including Sinn Féin senator Chris Andrews.

Israel has already blocked two attempts by activists to deliver aid by ship to Gaza, in June and July.

While the Israeli government has characterised the flotilla as a “selfie yacht”, Thunberg has pushed back against that criticism, telling the BBC on Sunday: “I don’t think anyone would risk their life for a publicity stunt.”

International aid agencies have been attempting to get food and medicine into the Palestinian territory but note Israel is restricting the flow of supplies.

Israel claims it is attempting to stop those supplies falling into the hands of Hamas. It and the US have backed an alternative food distribution system, the Gaza Humanitarian Foundation (GHF) which the UN refuses to co-operate with, describing its set-up as unethical.

A UN-backed group confirmed last month that there was famine in Gaza and the UN’s humanitarian chief said it was the direct result of Israel’s “systematic obstruction” of aid entering the territory.

Israeli Prime Minister Benjamin Netanyahu has called this an “outright lie”.

French Foreign Minister Jean-Noel Barrot said in a statement that France had ensured “that any possible boarding operation would take place under the best possible security conditions”.

Italy’s foreign minister said he had been reassured by Israel that its armed forces would not use violence against the 500 people aboard, including French and Italian politicians.

Antonio Tajani said: “The boarding was planned, we are talking about it… with [Israeli Foreign Minister Gideon] Saar so that there would be no violent actions on the part of the Tel Aviv armed forces, and this has been assured to me.”

Simon Harris, Ireland’s tánaiste (deputy prime minister), said his country “expects international law to be upheld and all those on board the flotilla to be treated in strict accordance with it”.

In Gaza, Israel is stepping up its assault on Gaza City as Hamas weighs its response to a new US plan to end the war. Arab and Turkish mediators are understood to be pressing Hamas for a positive response, but a senior Hamas figure has said the armed group is likely to reject it.

Israel’s Defence Minister Israel Katz issued a final warning to the hundreds of thousands of Palestinians in the city to evacuate southwards, saying those who remained during the offensive against Hamas would be “terrorists and supporters of terror”.

The International Committee of the Red Cross stated that “under international humanitarian law, civilians must be protected whether they stay or leave Gaza City”.