A Russian drone barrage targetted the centre of Kharkiv on Friday, injuring nine people and damaging a maternity hospital in Ukraine's second-largest city, officials said.

Mothers with newborns were being evacuated to a different medical facility, Kharkiv Mayor Ihor Terekhov wrote on Telegram. He didn't say whether anyone at the hospital was among the injured.

Russia's recent escalation of long-range Shahed drone attacks on Ukrainian cities, which often also include ballistic and cruise missiles as well as powerful glide bombs, has brought renewed urgency to efforts to improve Ukraine's air defences after more than three years of war.

"There is no silence in Ukraine," Ukraine President Volodymyr Zelenskyy said after the Kharkiv bombardment. Kyiv, the Ukrainian capital, has endured repeated and intensifying drone attacks in recent weeks, as have many other regions of the country.

June brought the highest monthly civilian casualties of the past three years, with 232 people killed and 1,343 wounded, the UN human rights mission in Ukraine said.