The Israeli navy has intercepted and boarded two boats which were trying to break the blockade of the Gaza Strip.
The Canadian and Irish boats with 27 campaigners from the United States and eight other countries on board, set sail from Turkey on Wednesday.
They were carrying medical supplies for the enclave.
The navy said no-one was hurt in the operation and the boats would be towed to the port of Ashdod, north-east of Gaza.
The boats are named Saoirse (Gaelic for freedom) and Tahrir (Arabic for liberation).
US officials also said Turkey had given assurances it would not send warships to escort the flotilla.
Ankara previously threatened to use its navy to escort boats to Gaza.
Israel tightened its blockade on Gaza in 2006 to stop the supply of arms or other items for military use.
The BBC reports imports of all weapons and military materials are banned, along with dual use materials such as fertilisers and certain chemicals.
There are also strict controls on building materials such as cement and steel cables. All exports are banned.
However, many types of goods are smuggled though tunnels under the Egypt-Gaza border.
