Russian overnight air strikes in Kiev have killed four people, local officials said.

The city’s mayor, Vitali Klitschko, said air defense systems had been deployed around the Ukrainian capital.

He added that windows were shattered in the Shevchenkivsky district, including at a metro station, and a fire broke out in a non-residential building. It’s unclear what the goal is.

Authorities warned of a ballistic missile threat and urged locals to seek shelter.