The Greek coastguard intercepted a boat carrying U.S. activists soon after they set sail from Greece on Friday to join a pro-Palestinian flotilla to Gaza, one of the activists said.

The boat, dubbed “The Audacity of Hope,” had just left Perama port, near Piraeus, for the open seas, a Reuters witness said.

A flotilla of boats planning to challenge Israel’s naval blockade of the Gaza Strip is expected to sail next week, after repeated delays that activists blame on Israeli sabotage. Israel has denied the accusations.

“We are just here, two miles off Piraeus. We’ve been stopped by the coastguard, their ship maneuvered in front of us and they are now talking to the captain, they want us to turn around,” Ann Wright, one of the activists, told Reuters.

“We are non-violent, we pose no threat,” she added, saying that the group was informed of the sailing ban just as it was setting off.

Greek authorities said earlier on Friday that ships bound for Gaza were prohibited from leaving Greek ports.

It was not immediately clear how the boat’s departure would affect the overall flotilla plans.

(Reporting by Renee Maltezou, Editing by Mark Trevelyan)