PRAGUE (AP) — An unknown perpetrator threw several Molotov cocktails at a Russian center in Prague promoting culture and history, Czech police said on Friday.

The incident in the Czech capital took place late Thursday and is now being investigated, they said.

The building of the center did not catch fire. A photo shows a broken window while two windows and a wall are partly covered with smoke.

Known as the Russian House, the building is funded by the Russian state but doesn’t have diplomatic status.

The center said it organizes various cultural, educational and scientific programs and offers courses in the Russian language.

Its director, Igor Girenko, told the Russian state news agency Tass that three of the six Molotov cocktails did not explode.

Russian Foreign Ministry spokeswoman Maria Zakharova, called it “a barbaric act,” the agency said.

The Russian embassy in Prague has asked the Czech authorities to boost security of Russian institutions and its employees in the country.

Czech Interior Minister Lubomír Metnar called the attack “unacceptable.”