The Global Sumud Flotilla said more than a dozen explosions were heard around the flotilla late Tuesday, with damage caused by "unidentified objects" dropped on deck.

Crosetto said he "authorised the immediate intervention of the Italian Navy's multi-purpose frigate Fasan, which was sailing north of Crete as part of Operation Safe Sea".

"The vessel is already en route to the area for possible rescue operations", he said in a statement posted on X.

The Global Sumud Flotilla (GSF) set sail from Barcelona this month with the aim of breaking the Israeli blockade of Gaza and delivering humanitarian aid.

Israel, which blocked two previous attempts by activists to reach Gaza by sea in June and July, has said it will not allow the flotilla to reach the embattled Palestinian territory.

"Israel will not allow vessels to enter an active combat zone and will not allow any breach of the lawful naval blockade," foreign ministry spokesman Oren Marmorstein told AFP.

"If their intentions are sincere, they should transfer any such aid to the nearby Ashkelon Marina so it can be forwarded promptly to the Gaza Strip in a non-violent manner," he said.

- 'Strongest condemnation' -

Several of the boats reported explosions Tuesday and unidentified objects being dropped on and near boats, causing damage and widespread obstruction in communications, GSF said.

It accused Israel of "endangering the 500+ unarmed civilians aboard the flotilla" that is carrying activists from 45 countries, including Swedish environmentalist Greta Thunberg.

"The drones that have been following us for days have detonated an explosive device, knocking off the boat's jib, and we're at risk of the mast falling," said Stefano Bertoldi, an Italian activist with the climate group "Ultima Generazione" (Last Generation) that is sailing in the flotilla.

Bertoldi issued several maydays as the explosions rang out, Last Generation said in a statement.

Crosetto expressed "the strongest condemnation" of the "attack" by "currently unidentified perpetrators".

Italian Foreign Minister Antonio Tajani said he had asked Israel to ensure the safety of "Italian citizens, along with members of parliament and MEPs".

He has already informed Israel that "any operation entrusted to Israeli forces must be conducted in compliance with international law and the principle of absolute caution," the ministry said in a statement.

Tajani has also asked the Italian Embassy in Tel Aviv to "reiterate its previous request to the Israeli government to guarantee the absolute protection of the personnel on board," it said.

The Global Sumud Flotilla currently numbers 51 vessels, most of which are off the Greek island of Crete.

Vessels waiting to join the flotilla had already been targeted in two suspected drone attacks in Tunisia.

- Maritime escort -

The Greek coastguard told AFP that a patrol boat from the EU borders agency Frontex had approached one vessel and saw no evidence of damage.

Contacted at its Warsaw headquarters, Frontex could not immediately confirm or deny the incident.

Italy's anti-establishment Five Star Movement, which has a senator on one of the boats, called on the EU "to intervene immediately to defend the vessels flying the flags of member states" by providing "protection and maritime escort through the deployment of Frontex vessels".

The pro-Palestinian Global Sumud Flotilla describes itself as an independent group not linked to any government or political party.

Sumud is Arabic word for "resilience".

Israel has launched a major air and ground offensive on Gaza City in a bid to root out Hamas after nearly two years of war.

During that time, Israeli military operations have killed at least 65,419 Palestinians, mostly civilians, according to the health ministry in Hamas-run Gaza, figures the UN considers reliable.

Hamas's attack that sparked the war resulted in the deaths of 1,219 people, mostly civilians, according to an AFP tally based on Israeli figures.