The Israeli navy boarded a ship and halted an attempt to break the sea blockade of Gaza on Saturday.
Forces stormed the ship and took the passengers into custody.
"The boarding was carried out only after numerous calls to the passengers onboard," an Israeli military statement said. "As a result of their unwillingness to cooperate and after ignoring calls to change course, the decision was made to board the vessel and lead it to the Port of Ashdod."
Prime Minister Benjamin Netanyahu praised the military operation.
"Their entire objective was to create a provocation and blacken Israel's name. If human rights were really important to these activists, they would sail to Syria," Netanyahu said.
The boat, named Estelle, was about 30 nautical miles off the coast of Gaza when it was stopped, said Reut Mor, an Israeli activist.
Passengers were hoping to call attention to human rights in the Palestinian territory, which has been under an Israeli blockade since 2007.
In addition to Mor, among those sailing are a priest and a lawmaker.
"The important thing is that they were on international waters and no one has the right to board the ship," said Victoria Strand, a spokeswoman for the ship. 'It is an act of piracy to board the ship in international waters."
The ship Estelle sails under a Finnish flag.