ATHENS, Greece (AP) — Protesters clashed briefly with riot police during an otherwise peaceful rally of 20,000 people in Athens Monday to mark the 41st anniversary of a deadly student uprising against the country's former dictatorship.

Police used tear gas and stun grenades to disperse a few dozen demonstrators who were breaking up paving stones to throw at officers, but no injuries or arrests were reported. Minor clashes between police and anarchists broke out later Monday in another part of Athens after the end of the march.

The annual march ends at the U.S. Embassy in protest of American backing for the 1967-74 dictatorship. This year it was policed by some 7,000 officers, deployed to prevent a potential repeat of violence seen in previous years. In recent rallies, protesters have also voiced anger at harsh austerity measures meant to shore up the battered economy.

The 1973 Polytechnic Uprising challenged the dictatorship, and police and the army responded by opening fire against demonstrators and bystanders around a central Athens campus. The regime collapsed the following year.