At least 10 people are reported to have been killed in a raid by Israeli commandos on a convoy of aid ships trying to reach Gaza.
Half a dozen boats carrying thousands of tonnes of aid were trying to break an Israeli blockade. The operation was organised by the Free Gaza Movement.
Turkey has already condemned the violence as unacceptable, with some of the ships flying Turkish flags.
Amid mounting criticism of the Israeli operation, the military says soldiers encountered serious physical violence by the protesters.
Some Israeli commandos are reported to have been slightly injured.
The captured ships are being taken to an Israeli port.
The flotilla set off in international waters off Cyprus on Sunday. It was organised, among others, by a Turkish human rights organisation. Ankara had urged Israel to allow it safe passage.