ATHENS — With the propeller shafts of two ships mysteriously damaged, the Greek authorities holding other vessels in port on government orders and an American boat turned back by the Greek coast guard on Friday just 20 minutes off the coast, the international flotilla to Gaza has stalled.

Organizers say they see the long arm of Israel behind their improbable woes, and while Israeli officials have dismissed such accusations as so much conspiracy mongering, they have declined to deny them outright.

One year after Israeli commandos killed nine Turkish activists aboard the Mavi Marmara during another flotilla, organizers had hoped once again to challenge the naval blockade of the Gaza Strip off its coast. It appears increasingly unlikely, however, that the eight boats now preparing to sail will ever be able or allowed to leave port.

Echoing a majority view among participants here, Johnny Leo Johansen, a ponytailed Norwegian photographer and activist, put it this way: “It’s like they’ve moved the blockade from Gaza to Greece.” On Friday the coast guard stopped the American boat in the flotilla, The Audacity of Hope, about one mile out to sea, quashing the initial excitement of the passengers, who were surprised to have been allowed to leave the harbor at all.