Several hundred youths hurled rocks, bottles and petrol bombs at riot police in central Athens following an annual march to mark the anniversary of a bloody student uprising.
The clashes, which went on for at least two hours late Tuesday, broke out following a rally that ended peacefully after being attended by 16,000 people and policed by 5,000 officers.
Violence also broke out in Greece's second largest city, Thessaloniki. There were no immediate reports of any injuries or arrests.
The annual march that ends at the US Embassy in Athens is held to commemorate the student uprising that was crushed by Greece's military regime in 1973.
Many Greeks blame Washington for backing the dictatorship that ruled Greece from 1967-74. [AP]