Police in Warsaw used rubber bullets and tear gas on Monday to break up groups of masked far-right youths when a march marking independence day turned violent.
Police said the groups torched cars, threw firecrackers and set fire to a guard's booth in front of the Russian Embassy - a symbol for some Poles of repression during Soviet rule. Four officers were hospitalized in the clashes and around a dozen people were detained.
"There is no justification for hooliganism," Poland's Foreign Ministry spokesman Marcin Wojciechowski wrote on Twitter, in an apology to Russia.
The march, initially peaceful, attracted several thousand protesters, many of whom chanted slogans brandished Polish flags, and chanted slogans such as "God, honor, fatherland." Some were calling for the resignation of the center-right government of Prime Minister Donald Tusk.
A few dozen then broke away from the group and attacked a city-centre building where left-wing radicals occupied a squat.
It is the third consecutive year the annual event commemorating Poland's national independence day has ended in clashes between rioters and riot police, prompting some Warsaw residents to call on city officials to ban it.
Elsewhere in the country, many Poles held peaceful events in memory of the country's regaining independence on November 11, 1918 following World War I.
The march coincided with the launch of the UN's COP19 climate change conference in Warsaw.
ccp/ch (AFP, Reuters, AP)