Israeli forces have intercepted 41 boats in an aid flotilla bound for Gaza, the voyage's organisers say, with 10 vessels still sailing towards the enclave.
The closest vessel to Gaza, Sirius, was about 270km away, the group said.
Israel's foreign ministry had said on X on Monday that it "will not allow any breach of the lawful naval blockade on Gaza".
Speaking in Ankara late on Monday, Turkish President Recep Tayyip Erdogan condemned the intervention against the "voyagers of hope" in the flotilla and called on the international community to act against Israel's actions.
Ships from the Global Sumud Flotilla had set sail for a third time on Thursday from southern Turkey after earlier attempts to deliver aid to Gaza were intercepted by Israel in international waters.
The group said there were 426 people taking part in the 54-vessel flotilla from 39 countries.
Israel's foreign ministry has called on "all participants in this provocation to change course and turn back immediately".