Troublemakers marred a gathering in downtown Buenos Aires in support of Argentina's gutsy performance in a 1-0 loss to Germany in the World Cup finals.
Clashes erupted between youths and the police late Sunday near the city's Obelisk monument, hours after what started as a peaceful rally.
Police used tear gas to disperse the rock-throwing crowd.
Officials say at least 15 police officers were injured in the skirmishes.
Police arrested more than 50 people.
**Russia blames Ukraine shelling for the death of Russian civilian**
Russia is blaming Ukraine for the cross-border artillery shelling death of a Russian civilian Sunday.
Local media reported that the man killed was called Andrey Shulyatyev.
His mother, Feoktista Chelikova, who was injured by the same blast, told Russian broadcaster RU-RTR that there were two shell impacts, the first landing behind the house.
The Kremlin threatened Ukraine with "irreversible consequences" for the death, which Moscow said came from an errant artillery shell. Ukraine has denied involvement, and said the shelling may have been the work of provocateurs seeking to trigger a Russian response.
Meanwhile, Russian and Ukrainian news reports say Ukraine forces attacked the perimeter of the rebel-controlled city of Luhansk Sunday with armored columns, pushing into the outskirts of the city but failing to recapture it.
Fighting has surged in the east since the Ukrainian government refused to renew a unilateral cease-fire June 30. Since then, Ukrainian forces have driven the rebels out of several cities, including Slovyansk, which was their main stronghold.