An aid ship has been diverted to Israel.
The country's foreign ministry says the British-flagged yacht Madleen is "safely making its way" to its shores, with passengers "expected to return to their home countries".
It's operated by the pro-Palestinian Freedom Flotilla Coalition, and was headed for Gaza, where humanitarian workers warn of impending famine.
The group released pre-recorded messages, alleging its members had been "kidnapped".
Climate activist Greta Thunberg is among those on board.
"I urge all my friends, family and comrades to put pressure on the Swedish government to release me and the others as soon as possible."