Warsaw police were searching on Monday for attackers who smashed windows in the city's Muslim cultural center.
The police were notified early Monday that some dozen windows were smashed during the night in the center that was opened in 2015 and includes a mosque, a meeting center, a shop and a restaurant. No one was hurt.
Warsaw police spokesman Mariusz Mrozek said CCTV was being reviewed to help identify the attackers and has appealed for people who might have any information about the attack to come forward. Muslim community leaders were to hold a news conference later in the day.
Warsaw's Muslim community has a few thousand members.
Acts of hatred and xenophobia are being reported more frequently in Poland since the Law and Justice party came to power two years ago. The government promotes Catholicism and refuses to take in non-Catholic refugees as part of an EU relocation plan.
In a separate incident, prosecutors have opened an investigation into a brief demonstration Saturday by a handful of right-wing radicals in the southern city of Katowice. They hung pictures of six European Parliament lawmakers from Poland who have supported a resolution condemning the government on symbolic gallows.
Deputy Prime Minister Piotr Glinski said the demonstration was "unwise and did not serve Polish democracy well."