The Greek coast guard has arrested the captain of a ship that was bound for the Gaza Strip to deliver humanitarian aid, dpa quoted Greek radio as reporting Saturday.
The captain of the Audacity of Hope vessel, who is accused of defying a ban on Greek or foreign ships bound for Gaza from leaving Greek ports, is to face a fast-track trial starting on Monday, according to reports.
Greece's coastguard on Friday intercepted the Audacity of Hope within its territorial waters.
Activist Vangelis Pissias said the US vessel had just left the Perama port, near Athens, when it was stopped by the Hellenic Coast Guard.
He said activists taking part in the international 10-ship flotilla will still try to leave Greek ports to break Israel's blockade of Gaza despite repeated delays that activists blame on Israeli sabotage.
Israel earlier denied allegations of sabotaging the Gaza-bound flotilla.
Israeli Foreign Ministry spokesman Yigal Palmor described the accusations as "ridiculous, paranoid," according to Ynet news online.
"The organizers didn't do the minimum required in order to prove that there was indeed sabotage; they didn't even file a complaint with the police. They live in a James Bond movie," Palmor was quoted as saying.
The activists have rejected Israeli claims that they are carrying dangerous materials or that they planned to use violence against Israeli soldiers trying to stop them at sea.
Several hundred pro-Palestinian activists from Greece, Canada, the United States and other countries planned to board the 10 ships - including two cargo vessels - carrying almost 3,000 tons of aid, medicine, a fully equipped ambulance and cement to Gaza.
On May 31, 2010, Israel's interception of the Freedom Flotilla I turned violent when naval commandos clashed with activists wielding knives and iron bars.