Police removed protesters blocking a march by members of a far-right youth organisation in central Warsaw on Tuesday, insisting they used force to protect a legal event.
Several hundred police officers were deployed to escort the march by around 100 members of the All-Polish Youth, a far-right Catholic nationalist group known for its opposition to abortion and gay rights.
The marchers, some wearing all black, touted red and white Polish flags and other green-and-white ones representing the ONR National Radical Camp, a Polish extreme-right party.
Chanting "Fascism is illegal", "Free Warsaw of fascists" and "No Pasaran" ("They shall not pass" in Spanish), around 200 opponents blocked their path, many by sitting down in the middle of the street.
Police used force to remove them, dragging some across the pavement, after verbal requests for them to move went unheeded.
No injuries were immediately reported and a police spokesman said no arrests were made.
"We took action against people whose behaviour disturbed a legal gathering," Warsaw police spokesman Sylwester Marczak told local media.
Poland's criminal code prohibits the promotion of fascist or other totalitarian ideologies.
The All-Poland Youth called the march on Tuesday to mark the anniversary of the 1920 Battle of Warsaw, when Polish forces defeated the invading Soviet Red Army.
Since taking office in 2015, Poland's rightwing populist Law and Justice (PiS) government has provided heavy police protection for street demonstrations organised by groups on the right of the political spectrum, including the extreme right.
Police also used force to remove protesters attempting to block an ONR march in April.
Around 2,000 officers were on hand last Thursday for a monthly march by PiS leader Jaroslaw Kaczynski in memory of his late twin brother, then president Lech Kaczynski, and 95 others killed in a 2007 jet crash in Smolensk, western Russia.
Anti-government activists staged a counter-demonstration, but police outnumbered them four-to-one.
The protesters believe Kaczynski, who insists the crash was no accident, has politicised the tragedy to gain the support of voters who share his views about its cause.
A probe by Polish and Russian investigators conducted before the PiS came to power in 2015 found that pilot error, bad weather and poor air traffic control were to blame for the crash.
However, a fresh probe by a new commission of inquiry set up by the PiS maintains that an explosion likely caused the aircraft to break up in the air before hitting the ground. It has not yet made public any evidence that would prove this conclusion.