|The captain is currently being held in police custody in Greece and is due to appear in court on Tuesday
The captain of a US ship bound for Gaza has been arrested by Greek authorities for a felony after being brought before a prosecutor, activists have told Al Jazeera.
The boat, which is part of a Freedom Flotilla aiming to break Israel's blockage of the Palestinian territory, set sail on Friday from the Greek port of Perama was towed back to shore by the Greek coast guard.
Jane Hirschmann, a member of "Jews Say No!" and national organiser for the boat, dubbed The Audacity of Hope, said the captain was being held in police custody and is due to appear in court on Tuesday.
Greece's coast guard said on Saturday that the captain of the Audacity of Hope faces charges of trying to leave port without permission and of endangering the lives of the boat's passengers.
Adam Shapiro, an International Flotilla committee organiser, speaking from Athens, told Al Jazeera: "The captain has been charged with a felony. Initially it [the charge] was a misdemeanour, but it has been upgraded to a felony."
The US boat is one of nine vessels carrying several hundred activists attempting to deliver aid to Gaza.
"The ship itself is currently in a naval compound, where it is being detained," Shapiro said.
"This is totally a political manoeuvre, nothing illegal about his mission. This has been orchestrated by the Israeli government and probably the US government," Hirschmann said.
"We are being tied up in all types of administrative deals."
Some of the passengers on the US ship have remained on board in solidarity with the jailed captain, Shapiro said.
On June 24, an anonymous complaint was filed against the ship's "seaworthiness". The Israel Law Centre (Shurat HaDin), took responsibility for the complaint in the Israeli media.
The Greek government put out a statement on Friday confirming that the Greek coast guard had enforced a decision by civil defence authorities to prevent all flotilla vessels from leaving Greek ports.
Greece's civil protection ministry said coast guard authorities had been ordered to take "all appropriate measures'' to implement the ban.
"By orders of the Hellenic Coast Guard Head Quarters to all local Hellenic Coast Guard Authorities, all appropriate measures are taken for the implementation of the said decision," the statement on the website of the Greek embassy in Washington said.
Shapiro said: "We [the International Flotilla committee], however, will continue to challenge this [the Greek ban] and we are challenging it this weekend politically.
"We have people working in the political scene here in Greece to put pressure. We are working on the legal options and we intend to sail still to Gaza."
Activists accuse Israel of damaging two other ships docked in Turkey and Greece that are part of a flotilla attempting to reach the Palestinian territory with humanitarian aid.
Yigal Palmor, Israel's foreign ministry spokesperson dismissed the sabotage charges on Saturday as "ridiculous," calling them "sad conspiracy theories".
Some journalists and activists on board an Italian-Dutch ship,the Stefano Chiarini , which also plans to take part in the flotilla, decided to leave on Saturday, while others were considering plans to protest against the Greek decision.
"Morale is low, really low. It is hard when plans keep changing all the time," Ewa Jasiewicz, a co-ordinator with the Free Gaza movement on board the boat, told Al Jazeera.
Some of the activists have been on the ship, which is docked at a port on the Greek island of Corfu, for over a week and are now planning to abandon the group to "attend to their daily lives", according to Khaled Turaani, a leading activist on the boat.
Turaani said he understood why some of the activists had taken the decision to abandon the group.
"It is not out of lack of commitment. They need to return to pressing issues related to their work," he said.
"This is not defeat. If every single activist would leave this morning, I believe the Freedom Flotilla has already served its purpose; namely, to expose the reality of the blockade on Gaza."
On Saturday, Turaani briefed the thinning group of activists about their options following the Greek blockade.
Turaani said there might still be a possibility to set sail with permission from the Greek authorities if the group changes the destination of the flotilla to the Egyptian port town of Al-Arish, near the Gaza border.
"Diverting the flotilla to Gaza in international waters is then a possibility," Turaani said.
"The Greeks are doing the bidding of the Israelis, but they should not also start diving into our conscience, and preemptively decide on what we might do."
The activists on Corfu have now decided to wait until Tuesday in hopes of a Greek reversal of their decision to block to the flotilla.
The remaining activists are discussing holding a protest on the ship without actually leaving the port.
"If they try to stop us we will show some civil disobedience," Turaani said.
Hamas, the Palestinian movement which controls Gaza, denounced Greece on Friday for intercepting The Audacity of Hope.
In a statement issued by its political leadership in Damascus, Hamas described the action as "inhumane" and said Greece had played into Israeli hands.
"This is inhumane action, is contrary to international regulations and norms," it said in a statement.
"Barring this aid from reaching the Gaza Strip is done as a result of pressure imposed by the Zionist occupiers [Israel]."
Hamas also called on the EU parliament and human rights organisations "to put pressure on the Greek government" to allow the flotilla to set sail to Gaza.