Violent clashes have taken place in the Polish capital Warsaw between police and rival marchers on the country's Independence Day.
Forty police officers were injured and 210 people were arrested, nearly half of them said to be "anti-fascism activists" from neighbouring Germany.
Nationalist marches have been growing in size on the national holiday, with leftists turning out to oppose them.
Police used water cannon and pepper spray to restore order.
They responded after right-wing marchers, many with scarves hiding their faces, began pelting them with stones, bottles and flares, national police spokesman Mariusz Sokolowski said.
Earlier, leftist demonstrators chanting "Fascism will not pass" attacked police as they tried to stop them blocking a major Warsaw thoroughfare, down which the nationalist march was due to pass, he added.
The police were attempting to keep Friday's nationalist and leftist demonstrators apart. A police plan to keep hostile marches from one another was successful, Mr Sokolowski said, but "thugs and hooligans joined the marches to target police".
Another police spokesman was quoted by AP as saying 14 police cars had been destroyed.
Of the 210 people arrested, 92 were found to be German citizens. Hanka Kubicka, a spokeswoman for anti-far-right movement the November 11 Agreement, said the Germans were "anti-fascism activists".
"They answered our call [to demonstrate] and our rallies were open to everyone," she was quoted as saying by AFP news agency.
Other foreigners detained during Friday's violence included a Dane, a Hungarian and a Spaniard, police said.
For weeks, a coalition of leftists, anarchists, pro-abortionists, Greens and gay-rights activists had been publicising plans to block the Independence March being organised by nationalist youth groups All-Polish Youth and the National Radical Camp, Reuters news agency reported.
A spokesman for Prime Minister Donald Tusk said he vowed to make sure those arrested for attacking police were severely punished.
Under Polish law, an assault on a law-enforcement officer carries a maximum three-year jail sentence.
This year the marches were seen as a major test of the country's security capabilities before the Euro 2012 football championship, which Poland will co-host with Ukraine next summer, the Associated Press reports.
The 11 November celebration marks the day in 1918 when Poland regained its independence, 123 years after it was divided between Russia, Prussia and the Austrian Empire.
Speaking at an official Independence Day ceremony earlier, President Bronislaw Komorowski had urged Poles to "celebrate this patriotic occasion together, not against one another".
Mr Komorowski honoured fallen veterans by laying a wreath at the Tomb of the Unknown Soldier during state ceremonies.