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Riot police in the Polish capital used truncheons and rubber bullets to break up a crowd of right-wing extremists who pelted them with firecrackers and lumps of concrete at a parade to mark the national holiday.
Thousands of police in riot gear had earlier lined the streets of Warsaw to try to stop right-wing nationalists and radical left-wing groups from using the independence day holiday as an opportunity to fight each other.
It was the second year the celebrations have degenerated into violence, underlining the deep gulf between those who want a conservative, religious society that rejects foreign influence and those who want Poland to join the European mainstream.
As demonstrators gathered for a right-wing independence day rally, young men with their faces covered by scarves chanted nationalist slogans and railed against supposed Jewish conspiracies.
" We are Poles, that is why we came here. Poland is going in ... the direction of dependency, energy dependency, economic dependency," said a demonstrator who gave his name as Wojciech.
The fighting started when some of the right-wing protesters threw firecrackers and projectiles at police in riot gear who had cordoned off the area.
A Reuters correspondent saw police respond by beating protesters with truncheons. Some demonstrators tore off chunks of concrete at a construction site to use as missiles. Police said they had also used rubber bullets. A spokesman said two police were injured, including one who was hit on the head with a bottle.
"Some people mixed into the head of the march and .... attacked police with stones, bottles and flares. We responded with rubber bullets and pepper gas," the spokesman, Mariusz Sokolowski, told Polish television.
Polish President Bronislaw Komorowski, addressing the official independence day parade in Warsaw a few hours before the violence broke out, appealed for a less polarised society.
"Today public life is poisoned by excessive rows," he said. "We should be critical, but criticism should not mean mutual destruction."
On the same date last year, right-wing demonstrators fought pitched battles with police who were trying to prevent them attacking a counter-demonstration by left-wing radicals.
Poland, the biggest economy in eastern Europe, is experiencing a period of peace and prosperity unusual for a country with such a turbulent history.
Prime Minister Donald Tusk, a liberal, is credited by many Poles for bringing political stability. But the predominantly Catholic society is deeply split over issues such as abortion, gay rights and how deeply to integrate with the European Union.
Most of the time the argument is conducted in reasonably civil terms. However, extremists on the margins of each camp sometimes get violent.