The organisers of an activist flotilla bound for Gaza said on Tuesday Israeli forces had intercepted 41 of their boats in the eastern Mediterranean, with 10 vessels still sailing toward the enclave.
The closest vessel to Gaza, Sirius, was 145 nautical miles away, the group said.
Israel's foreign ministry had said on social media on Monday that it, "will not allow any breach of the lawful naval blockade on Gaza".
Speaking in Ankara late on Monday, Turkish President 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, in a rather hypocritical statement.
Ships from the Global Sumud Flotilla had set sail for a third time on Thursday from southern Turkey, after earlier attempts to break the Gaza blockade 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".
(Reporting by Daren Butler; Editing by Timothy Heritage, Baird Maritime)