A Canadian-organized ship carrying protesters bound for the blockaded Gaza Strip has been prevented from leaving a port in Greece.

Greek coast guards boarded the ship Friday and attempted to arrest Canadian Sandra Rush, a member of the organizing committee Canadian Boat to Gaza, for refusing to surrender the boat's registration papers, the protesters said.

The Audacity of Hope sits docked in the town of Peramat after it was intercepted Friday. Greece has banned ships heading to Gaza from leaving Greek ports. (Darko Bandic/Associated Press)

Another vessel bound for Gaza carrying mainly U.S. activists made it three kilometres out to sea but was intercepted by the Greek coast guard and brought back to shore, as Greece announced it was banning vessels heading to Gaza from leaving Greek ports.

The Canadian ship, known as the Tahrir, is part of a flotilla of nine Greek and foreign-flagged vessels that have been planning to break Israel's sea blockade and deliver aid to the Palestinian territory.

Canadian organizers with the flotilla said they aren't breaking any laws and will continue attempts to sail to Gaza.

"It is the blockade of Gaza that is illegal under international law," organizer Dylan Penner said in a statement.

"We have a legal and moral obligation to challenge the blockade, given the failure of the international community to act."

U.S. ship sneaks away

The secretive attempt by the U.S. activists' ship, called the Audacity of Hope, to head out to sea ended in failure after authorities in inflatable speedboats raced after them when their vessel tried to sail without permission from the port of Perama, near the Greek capital, Athens.

"We shall overcome," the activists sang as security personnel watched from their boat just 10 metres away, according to updates protesters posted on the internet during a brief standoff.

The Irish ship Saoirse, in dry dock in Turkey, is alleged to have been sabotaged by Israeli agents before it could sail to Gaza. (Agence France-Presse/Getty)

Greek officials appealed to them to turn around, arguing that it was not safe to continue, but activists responded that it was not safe in port because of fears of sabotage of their vessels, organizers said.

On Thursday, an Irish ship, the MV Saoirse, said it had to abandon plans to set sail from the Turkish town of Gocek because of Israeli sabotage. Earlier this week, activists said the propeller of a Swedish ship in a Greek port was sabotaged. Israel has not commented on the reports.

Flotilla organizer Vangelis Pissias condemned the Greek ban on Friday and argued the government had no legal grounds to block private vessels that were heading to international waters from its ports.

"The efforts to sail will continue," he said.

Israeli pressure on Greece alleged

Many of the passengers on the Canadian and U.S. boats are Jewish; the ships also include Muslims and people of other faiths, as well as high proportions of women and people over age 50, organizers said. Filmmaker John Greyson and Quebec activist Manon Massé are among the Canadian vessel's delegates, while the U.S. boat's passengers include two former U.S. military officers.

The Greek government action delivered a major blow to the flotilla and its several hundred activists. The setback followed a week of administrative delays that organizers attributed to Israeli pressure on Greece, which is mired in an economic crisis and has grown closer to Israel as it seeks more foreign investment.

Israel has said it will thwart any effort to breach its sea blockade of Gaza, which it imposed on the Palestinian territory after the militant and political group Hamas took control of it in 2007 following its victory in parliamentary elections the year before.

The U.S., EU, Canada and Israel consider Hamas a terrorist group.

Hamas issued a statement Friday condemning Greece's ban on sailings to Gaza, saying Athens had bowed to Israeli pressure and was acting in an "inhumane" manner "contrary to international regulations and norms," according to the Agence France-Presse news agency.

An Israeli raid on a similar flotilla last year killed nine activists on a Turkish ship, with each blaming the other for the violence. Israel says its sea blockade stops weapons from reaching Iranian-backed Hamas militants.

With files from CBC News and The Associated Press