A mosque in the Czech Republic's second city of Brno has been vandalised with graffiti threatening to kill Muslims, police said on Saturday.
"Don't spread Islam in the Czech Republic! Or we'll kill you," read the inscription sprayed on the mosque.
"We have been investigating the case since Friday afternoon as damage to property for now," local police spokesman Bohumil Malasek said.
The perpetrator faces up to a year in prison if convicted.
"We take it seriously as a direct threat, it's not an anonymous call on the internet," Muneeb Hassan Alrawi, head of the Czech Muslim Communities Centre, told the CTK news agency.
"We must also see this in the light of attacks on mosques in the world and of the oppressive sentiment and atmosphere in the Czech Republic," he added.
The migrant wave that peaked in Europe in 2015 stoked anti-Muslim sentiment in the Czech Republic even though it is home to only a tiny number of refugees.
The Muslim population in the Czech Republic, an EU member of 10.7 million people, tallied at 3,358 in a 2011 census but unofficial estimates suggest a community of 10,000-20,000.
Islamophobia has been steadily on the rise in the eastern European country in recent years, according to a 2018 study.
The most notable rise in anti-Muslim sentiment has been in public discourse and on the internet, the European Islamophobia Report 2018 noted.
"The content that would be considered extreme or fringe a couple of years ago is now given a platform in the Czech Senate and other public spaces," said the report, adding that fake news and hoaxes related to Muslims have also proliferated, sparking an increase in far-right radicalisation.
The Czech Republic made its first conviction for terrorism in January 2019 after a pensioner was found to have chopped down trees which fell onto train lines, leaving messages at the scene proclaiming "Allahu Akbar" - or "God is great" in Arabic - so as to fake an Islamic extremist terror attack.