A small ship bound for Gaza eluded the Greek coast guard, while a second was intercepted and returned to port.
The small ship, a French boat with eight protesters aboard, left Greek waters Tuesday as the first vessel of a Gaza-bound flotilla attempting to break the Israeli naval blockade of the coastal strip.
The Dignite al Karama will arrive in international waters near Gaza in about two days, the French news agency AFP reported.
On Monday night, the Canadian ship Tahrir was seized by the Greek coast guard minutes after leaving from the port of Agios Nikolaos near Crete. Two of the Canadian passengers and an Australian passenger, who attempted to throw off the coastguard by sailing kayaks near the ship, were arrested.
The ship reportedly was damaged when it slammed into a concrete pier as it was returned to port.
Also Tuesday, activists from the Spanish flotilla boat reportedly occupied the Spanish Embassy in Athens after meeting with their ambassador to ask their government to pressure the Greek government to allow them to sail.
Leaders of the Gaza-bound flotilla rejected an offer by Greece to deliver aid from the ships stuck in Greek harbors to the coastal strip either through Egypt or Israel, a deal to which Palestinian Authority President Mahmoud Abbas reportedly had agreed.
The ships were to have marked the May 31, 2010 raid of a similar flotilla by Israeli commandos. Nine Turkish activists were killed in the subsequent melee, including a Turkish-American dual citizen.
Israel says the flotilla is illegal and military action to keep it from arriving in Gaza is legitimate. Israel maintains the blockade to keep weapons from flowing into Gaza, which is controlled by Hamas, and also as leverage to secure the freedom of Gilad Shalit, a kidnapped soldier held by Hamas since 2006.
Human rights groups say the blockade keeps out basic foods and medicines, although the Obama administration says its conditions have eased considerably in the last year.