KYIV, Ukraine (AP) — Four people died in a a fire in a psychiatric hospital in eastern Ukraine, local police said Monday.

Police said the fire broke out overnight in a ward at the Starobilsk hospital in the region of Luhansk. It wasn’t immediately clear what caused the blaze.

Firemen battled the flames for two hours, while police and the hospital’s medical personnel evacuated people.

Aside from those who died, three people have sustained injuries.

An investigation into what caused the fire has begun.