American activists set sail from Greece on Friday aboard a boat Set to take part in a pro-Palestinian flotilla to Gaza, defying calls from Israel to cancel and a ban by Athens.

The boat, dubbed "The Audacity of Hope" left Perama port for the open seas, a Reuters witness said. Greek authorities said earlier on Friday that ships destined to Gaza were prohibited from leaving Greek ports.

The boat left behind the rest of a pro-Palestinian international flotilla.

Nearly 300 pro-Palestinian activists from 22 countries including Canada, France, Greece, Ireland, Italy and Spain are set to join the flotilla, among them dozens of middle-aged and elderly Americans and Europeans.