ATHENS, (AFP) — Coastguard officials intercepted a US vessel Friday after it tried to defy a Greek ban on boats sailing to Gaza, as activists accused Israeli agents of a campaign harassment and sabotage.

The Audacity of Hope sailed without warning, leaving behind nine other boats supposed to be taking part in the 2011 international “Freedom Flotilla,” after the Greek authorities announced their ban.

It was quickly intercepted by a coastguard boat with six masked, armed men on board.

As the news spread that the US boat had been stopped, activists slammed what they called an “out-sourcing of Israeli foreign policy.”

The French “Boat to Gaza” organisation released a statement claiming that Israeli Prime Minister Benjamin Netanyahu had thanked Greece and other leaders around the world for their stand against the “provocative flotilla”.

Activists have also blamed Israel for the sabotage of two of their boats and for a campaign of harassment and dirty tricks against activists.

Irish vessel the Saoirse pulled out of the mission after it was damaged in an attack while moored in Turkey.

And technicians in Piraeus port near Athens were rushing to fix the Swedish-owned Juliano, which had also been sabotaged on the weekend.

Israel has flatly rejected accusations of skullduggery as “paranoid.” A foreign ministry spokesman accused the activists of “living in a James Bond film”.

But Israeli has repeatedly said it is determined to stop the flotilla and on Thursday urged defiant organisers not to create “new friction” in the region.

Flotilla activists’ called for Greece to resist Israel’s diplomatic pressure.

But on Friday, the Greek coastguard announced that the Gaza-bound mission could not leave their ports — at least for the moment.

“The departure of ships with Greek and foreign flags from Greek ports to the maritime area of Gaza has been prohibited today,” the coastguard said in a statement released Friday, an hour before the ship set sail.

“All appropriate measures” should be taken to implement the ban, it said.

When the Audacity tried to break the ban, they were quickly intercepted and escorted back to Keratsini port on Friday evening, said a spokesperson for the activists.

“Six masked men on a Greek coastguard boat came up along side and pointed their weapons at the passengers,” said Jane Hirschmann, forcing the captain to turn back “for the saftey of everyone on board.”

On Friday morning, US activists had rallied outside the US embassy in Athens to protest what it said was America’s “complicity” with Israel in moving to block the flotilla in Greek ports.

Activists of all ages chanted “Gaza we are coming!” and “Free, free Palestine”, as Greek police pushed them back with riot shields.

But even before the Greek authorities announced the ban, all the boats committed to the flotilla were still waiting for clearance to leave, after after complaints were filed against them.

The Audacity was one of them.

The vessel, which is carrying 3,000 letters of support for Palestinians, had been refused permission to sail after an Israeli law firm lodged a claim that it was not seaworthy.

Activists on the other boats meanwhile would not say if they too would try to defy the authorities and break for the open seas later Friday or early Saturday.

But the tensions thus far are as nothing to last year’s clash.

In May 2010 Israeli troops ended a similar attempt by a multi-national flotilla to reach Gaza when they stormed the lead vessel, killing nine Turkish activists and sparking a diplomatic storm.

But Dror Feiler, a Swedish organiser and representative of the European Jews for Just Peace organisation, said they were undeterred.

“We will continue preparing our boats, our work has just begun,” he said.