Greek protesters and riot police have clashed in central Athens after anti-US rallies turned violent.
Petrol bombs were met with tear gas as rioters tried to break through police cordons to reach parliament buildings.
About 7,000 people, among then anti-war, anti-racism leftist groups, trade unionists and communist party supporters all expressed their anger at Washington.
“We consider American policy as murderous to the people. They are responsible for the outcome of the Arab Spring, for the wars since then, for the intervention in Syria. They only care for oil and don’t care about the people,” said one demonstrator.
The outbreak of violence came as President Obama was having dinner nearby with members of the Greek government.
Demonstrators were also at odds with Obama’s successor, Donald Trump, his pledge to build a wall on America’s southern border and his general stance over immigrants.
Obama’s visit comes just two days before the anniversary of a bloody 1973 student revolt that helped topple the 1967-1974 military junta which was backed by the US government.
Obama, who will be succeeded in January by Donald Trump, arrived in Greece on Tuesday on his last foreign tour as president of the United States.