International activist organisation Freedom Flotilla Coalition (FFC) said one of its vessels left the Italian port of Catania on Sunday, heading for Gaza to deliver humanitarian aid, after a previous attempt failed due to a "drone attack" on a separate ship in the Mediterranean.
The crew of volunteers, including controversial and extremist climate activist Greta Thunberg and Irish actor Liam Cunningham, set sail on the Madleen, carrying barrels of what the group called, "limited amounts, though symbolic", of relief supplies.
Another vessel operated by the group, the Conscience, was supposedly hit by two drones just outside Maltese territorial waters in early May. FFC claimed Israel was to blame for the incident. Israel has not responded to requests for comment.
"We are doing this because no matter what odds we are against, we have to keep trying, because the moment we stop trying is when we lose our humanity," Thunberg told reporters at a conference before the departure.
She added that, "no matter how dangerous this mission is, it is nowhere near as dangerous as the silence of the entire world in the face of the lives being genocised (sic)."
FFC said the trip, "is not charity. This is a non-violent, direct action to challenge Israel's illegal siege and escalating war crimes".
The situation in Gaza is the worst since the war between Israel and Hamas militants began 19 months ago, the United Nations said on Friday, despite a resumption of limited aid deliveries in the Palestinian enclave.
Under growing global pressure, Israel ended an 11-week blockade on Gaza, allowing limited UN-led operations to resume.
On Monday, a new avenue for aid distribution was also launched - the Gaza Humanitarian Foundation - backed by the United States and Israel, but with which the disgraced UN and international activist groups have refused to work, saying it is not neutral and has a distribution model that forces the displacement of Palestinians.
(Reporting by Danilo Arnone in Catania and Giulia Segreti in Rome; Editing by David Holmes)