"Since the promises made by the Russian delegation about reducing the intensity of strikes in Kyiv and Chernihiv, we have actually been observing an increase in intensity of shelling and mortar attacks. And over the past 24 hours ... our hospitals have received 20 injured people, and this is both military and civilians," Mayor Vladyslav Atroshenko told during an interview from a hospital.

Read here Parts of the Kharkiv region are under "constant shelling"

Patients are in the hallway of the hospital because it is currently the safest place, away from windows, he said.

While Russian troops are moving back toward the border, artillery strikes and mortar attacks are increasing, he said, and officials overnight saw multiple Russian planes cross into Ukrainian airspace toward Chernihiv.

"The Russians are using mortars — which is like a very old, very old weapon — and it is not a precision weapon, and they're shooting mortar shells at us, four or five kilometers away from the city ... and also flying aircrafts and dropping bombs from a low height, so aiming deliberately at the destruction of civilian populations and residential neighborhoods," he added.