Some 2,500 people brandishing banners denouncing US imperialism and claiming "Obama non grata", or not welcome, were blocked from heading toward the site where Obama was meeting Greek Prime Minister Alexis Tsipras .
Demonstrations in central Athens were banned for the two-day visit by Obama, who heads afterward to Germany, then Peru, in his last diplomatic tour.
The protesters -- described by police as made up mostly of leftists with some 400 anarchists -- backed off, with some setting light to waste bins before eventually dispersing half an hour later.
The anarchist movement is very active in the Greek capital and their protests often end in scuffles with police and damage to surrounding buildings and infrastructure.
At the time of the protests, Obama was dining at the presidential palace alongside Tsirpas and Greek President Prokopis Pavlopoulos .