Organisers of a Gaza-bound flotilla said they have not abandoned their plans to breach Israel's sea blockade of the territory despite a Greek government ban on their vessels leaving the country's ports.
The campaign experienced a major setback when Greece announced its restrictions on Friday, and authorities arrested the captain of a boat carrying American activists that tried to leave Greece without permission.
However, co-ordinators of the flotilla were trying to maintain momentum with small protests in Athens in the face of increasing calls for them to scrap their campaign.
On Saturday, the Middle East Quartet of Mideast mediators - the US, UN, EU and Russia - urged governments to discourage Gaza-bound flotillas that could escalate tension in the region.
Several protesters from the American vessel briefly protested outside the US Embassy before leaving.
They had originally planned to stay there overnight. They want Washington to pressure Greece to release their American captain, John Klusmire, and allow them to depart for the Gaza Strip.
The US Embassy provided standard consular services to the American citizens in the flotilla "before and after" the interception of their vessel, spokesman Stuart Smith said.
The Obama administration had warned American activists against participating in the flotilla, saying they might be violating US law because Gaza is run by the militant Hamas group, a US-designated foreign terrorist organisation.
Greek activist Dimitris Plionis said there would be "some action" at the beginning of the week, but he did not specify what the pro-Palestinian activists were planning to do, presumably because Greek authorities might try to thwart their efforts.
"The ban is there and we have already said that we are still considering to sail," Mr Plionis said. "This story is not finished."
Without elaborating, he noted that "ships are free to go to other locations" besides Gaza.
The comment raised the possibility that organisers have debated whether their vessels could declare they are bound for another destination, and then turn toward Gaza once they are in international waters.
The flotilla has planned to carry medicine, construction equipment and other aid to the coastal strip.