Polish police issued a public appeal for witnesses Monday after unknown attackers smashed windows at a Muslim cultural center in the capital Warsaw, while prosecutors opened a probe into a far-right protest in the south of the country over the weekend.

About a dozen windows were shattered overnight at the Muslim center, which opened in 2015 and includes a mosque, a meeting center, a shop and a restaurant. No one was hurt.

"I am 100 percent sure this was a racist, anti-Muslim attack," Muslim community leader imam Youssef Chadid told a news conference.

He blamed it on "not very friendly" atmosphere in Poland now that misrepresents Islam and appealed on the government to speak against attacks on Muslims.

"If the government says nothing on the issue, there will be no progress," despite declarations of tolerance, Chadid said.

Warsaw police spokesman Mariusz Mrozek said security footage was being reviewed to help identify the culprits, and appealed for people who might have any information about the attack to come forward. At least two people are seen in the footage, Muslim leaders said.

Warsaw's Muslim community is made up of about 22,000 people with two mosques, including the one at the center that was attacked. About 500 people come to pray in the center's mosque, the leaders said.

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-Christian refugees as part of an EU relocation plan, citing security concerns.

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. The protesters hung pictures of six European Parliament lawmakers from Poland who have supported a resolution condemning the government on symbolic gallows.

Prime Minister Beata Szydlo condemned this "act of aggression and intolerance" and insisted the lawmakers were safe in Poland.

Deputy Prime Minister Piotr Glinski said the demonstration was "unwise and did not serve Polish democracy well."

The President of the European Parliament, Antonio Tajani, said on Twitter that he would write to Szydlo "to ensure the security of elected Members of the European Parliament to express their opinions independently, without threat."

He urged Szydlo to "oppose those who spread hatred by exhibiting outrageous pictures of hanged politicians."