An aid ship carrying eight Jewish activists from Europe, Israel, and the US was apprehended by the Israeli navy just miles off the coast of Gaza after being warned by a warship.
Navy commandos boarded the Irene, and then the passengers were led off the boat.
Rich Cooper, an organiser with Independent Jewish Voices, told Al Jazeera that his group is now demanding the immediate release of the activists.
The ship had left the port of Famagusta in Turkish-held northern Cyprus on Sunday afternoon.
The Israeli army had said it would offer to transfer the ship's aid supplies to the port of Ashdod and then ask the crew to turn back.
Ehud Barak, Israel's defence minister, had repeatedly warned that Israel will intercept any ship nearing Gaza, which is governed by the Palestinian group Hamas.
"In the tradition of the civil rights movement ... we assert our right to continue to Gaza under international law," Glyn Secker, the Irene's captain, told Al Jazeera on Monday.
The 10-metre catamaran was tiny in comparison with the six-ship May 31 aid convoy that contained 10,000 tonnes of aid and over 700 activists.
But the voyage was a gesture by left-leaning European Jewish groups to highlight what they see as a flawed Israeli policy of collective punishment against 1.5 million Palestinians in Gaza.
Yousef Rizka, a Hamas official, said: "The government has received Jewish activists heading to Gaza before. The government positively views all attempts to break the siege on Gaza".
Israel eased its naval blockade following harsh international condemnation for storming the Mavi Marmara. The nine deaths aboard the Freedom Flotilla were a public-relations disaster for Israel.
Since then, groups from Iran, Ireland, Lebanon, and Libya, among others, have been trying to reach Gaza - with varying degrees of success.
Groups represented on board the Irene included the UK-based Jews for Justice for Palestinians and the German Jewish Voice organisation.
"The boat's cargo includes symbolic aid in the form of children's toys and musical instruments, textbooks, fishing nets for Gaza's fishing communities and prosthetic limbs," read a statement from European Jews for a Just Peace movement, the activist network that co-ordinated the voyage.
"We stand in the proud Jewish tradition of justice, of championing the rights of the downtrodden, of implacable opposition to prejudice and racism."
Kate Katzenstein-Leiterer, a leader of the German Jewish Voice, was quoted in June as saying, "We want Israel to behave in a way that it can be recognised as a democratic state. Now it is recognised as a criminal state. That is not what we want."
Reuven Moskovitz, an 82-year-old Holocaust survivor among the passengers on the British-flagged vessel, is a founding member of the Jewish-Arab village Neve Shalom (Oasis of Peace).
"We are two peoples, but we have one future," Moskovitz said in a statement on the Jewish Boat to Gaza website.
Another passenger was Rami Elhanan, an Israeli whose daughter died in a 1997 suicide bombing at a Jerusalem shopping centre.
Eli Osherov, a reporter from Channel 10 in Israel, was also on board.
Andy David, Israel's foreign ministry spokesman, described the voyage as "a provocative joke that isn't funny".
Secker, the Irene's captain, told Al Jazeera Monday that the organisers had "a particular point to make, as the voice of Jews who have an alternative opinion to that of the Israeli establishment".
Source: Al Jazeera and Agencies