KYIV, Ukraine (AP) — A series of explosions were heard in Kyiv on Saturday morning before the air raid sirens were turned on.

Deputy head of Ukraine’s presidential office Kyrylo Tymoshenko said on Telegram that a missile attack on critical infrastructure in the capital was underway.

Kyiv mayor Vitali Klitschko said that “explosions were heard in Dniprovskyi district, left bank of Kyiv.”

It wasn’t immediately clear whether the explosions were caused by the strikes or by air defense systems operating. The Ukrainian capital hasn’t been attacked since New Year’s night.