Rocks were hurled at officers during a rally held by ultra-nationalist political parties in central Warsaw, although organizers blamed the trouble on outside agitators.
Polskie Radio said the trouble only lasted a short time, but was a repeat of more-serious rioting that broke out in Warsaw a year earlier.
The nationalist protesters appeared to be no less angry at the Polish government. Banners decrying the European Union and championing "Polish independence" were seen in the crowd along with one calling Prime Minister Donald Tusk "a moron."
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