Czech police say unknown attackers have set a refugee center on fire in the Czech capital of Prague, injuring one person.

Spokeswoman Iveta Martinkova says about 20 people attacked the Klinika center in Prague's No. 3 district with Molotov cocktails Saturday about 7:30 p.m. She says it's not clear who was behind the attack and police are investigating. The attack took place just hours after thousands of people rallied in Prague against Muslims and immigration.