ATHENS (AFP) - Thirty pro-Palestinian activists on a Canadian boat bound for Gaza that was stopped out of a Greek port Monday for breaking a ban, defied authorities by claiming they had all captained the ship. Greek coastguards halted the Canadian vessel Tahrir about 10 minutes after it left port on the island of Crete Monday afternoon with some 40 people on board, organisers said. "We have been boarded by about 15 armed special forces," David Heap of the Canadian Boat to Gaza organisation told AFP by phone from the vessel. "I'm being blocked by a man with a machine gun," he said over the noise of shouting from passengers he said were being pushed around. "We are not using force back," he added. The Tahrir, which was carrying activists from Canada, Belgium, Italy, Switzerland and Turkey, was forced to turn back to Aghios Nikolaos port in Crete, as Heap and others shouted, "We have to go to Gaza. Let us pass" It had sailed without a captain in the hope of avoiding a severe legal repercussions. Passenger Joseph Dube, a former Belgium senator with an expired captain's licence, had sailed the ship and agreed to take full legal responsibility, according to the Tahrir's spokesperson Huwaida Arraf. When authorities boarded the boat and demanded to speak to the captain, some 30 passengers "claimed they were the captain," she said. "Everyone took part in manning the boat in one way or another -- they all had a go at sailing it. The idea is that it will be difficult to arrest 30 people," she said. The Canadian boat was the second in the Freedom flotilla to attempt to set sail. The US Audacity of Hope boat had been thwarted Friday by authorities imposing a ban this week on all Gaza-bound ships leaving Greek ports. Its American captain John Klusmer was arrested Friday after his ship was intercepted in Greek waters and is due to appear before a prosecutor on Tuesday in the port of Piraeus near Athens. It is not yet clear what will happen to the passengers on the Tahrir.