A Russian air attack on Ukraine's western city of Lviv, not far from the border with NATO member Poland, has killed seven people, including three children, Mayor Andriy Sadovy said on the Telegram messaging app.

The strikes came a day after the war's deadliest single attack this year, when Russia hit a military institute in the central town of Poltava with two ballistic missiles, killing 50 and wounding hundreds more.

Among those killed in Lviv by the drone and missile attack was a 14-year-old girl, early details showed, with five children among the injured, the regional governor, Maksym Kozytskyi, said on the Telegram messaging app.