The demonstrations followed several reported attacks and verbal confrontations involving Ukrainians.
They also came amid evidence of a sharp increase in anti-Ukrainian content on Polish social media.
Participants in the "Good Neighborliness" rally outside the Ukrainian embassy in Warsaw carried Polish, Ukrainian and Belarusian flags.
They chanted "Don’t let them divide us," and displayed signs reading "Stop hate" and "We are with you, with all our hearts."
Organizer Dzmitry Hałko, a Belarusian former war correspondent in Ukraine and disinformation analyst, said the gathering was a spontaneous response to a series of xenophobic incidents in Poland.
"We cannot defeat bots online because troll farms always create the illusion of a numerical advantage," Hałko told Poland's PAP news agency.
Troll farms are coordinated networks of fake or automated accounts used to manipulate public debate.
"Bots do not take to the streets; real people do," he added.
Hałko said a nationwide Friendship March was planned for August or September.
Jerzy Wójcik, publisher of the Polish-Ukrainian current-affairs website Sestry.eu, said Poland's political and online debate had shifted attempts to turn Poles against Ukrainians by fomenting resentment.
"Someone finally had to come out and say loudly: 'Stop, enough of this,'" he said. "If we allow this spiral to continue, it will end in a terrible disaster for relations between our countries."
A separate rally on Wrocław’s Market Square drew about a dozen people, the PAP news agency reported.
Participants called on the public to respond to verbal and physical aggression against Ukrainians.
"We must resist this, we ordinary people, rather than organizations or parties," organizer Ewa Trojanowska said. "We unconditionally support Ukraine in its struggle. We leave history to historians."
Poland has hosted a large Ukrainian community since Russia launched its full-scale invasion in February 2022. Relations have occasionally been strained by historical disputes, political rhetoric and arguments over economic support for refugees.
Recent incidents included the verbal abuse of three Ukrainian females, including two 11-year-old girls, on a city bus in Bielsko-Biała, southern Poland. A 54-year-old man was charged in the case.
In the southern city of Gliwice, a masked attacker reportedly beat a 46-year-old Ukrainian man with a baseball bat. A video also circulated online showing radical activists entering the office of a Ukrainian company.
A report published in late June, We Are Not at Home: Ukrainian Migrants and Refugees on Relations With Poles, also warned of growing anti-Ukrainian sentiment.
It was compiled by migration researcher Olena Babakova and University of Warsaw sociologist Przemysław Sadura.
The Res Futura analytical center examined nearly 520,000 social media posts published in May. It found that anti-Ukrainian messages had increased sharply, while comments favorable toward migrants accounted for about one in every 1,000 posts.
In recent weeks, Russian disinformation operations have intensified. They have focused heavily on the World War II-era Volhynia massacres, one of the most sensitive issues in Polish-Ukrainian relations.
Poland’s Resilience Council said Russia’s Federal Security Service (FSB) circulated supposedly newly declassified documents alleging the murder of 11 Catholic priests and 2,000 residents of Volodymyr-Volynskyi in 1943.
Polish historians said the event described did not take place and that the account appeared to combine separate incidents.
Fact-checkers also identified activity by the pro-Russian Matryoshka and Storm-1516 networks, which distributed videos imitating Western news organizations.
These included a fabricated France 24 report claiming that Ukrainian President Volodymyr Zelensky had allocated EUR 70 million for a memorial to the Ukrainian Insurgent Army (UPA), whose members were responsible for massacres of Polish civilians.
The Polish government said the campaign was intended to transfer anger over WWII crimes into present-day relations and deepen hostility between Poles and Ukrainians.
Other faked material has sought to portray Ukrainians living in Poland as dangerous, ungrateful or hostile.
Separately, Polish prosecutors announced charges against an 18-year-old Ukrainian accused of carrying out 47 assignments for Russian intelligence, including desecrating memorials to Polish victims of the UPA.
Poland's Internal Security Agency (ABW) said the purpose was to provoke conflict between Poles and Ukrainians, demonstrating how online propaganda can be reinforced by planned incidents in the physical world.
(rt/gs)
Source: IAR/PAP