Russia launched missile and drone strikes on Ukraine's second-largest city of Kharkiv, killing six and injuring 11, Mayor Ihor Terekhov said on Saturday.

Ukraine's National Police released images of the damage caused by the attack, including fires that had broken out on the streets and next to buildings.

Attacks on Kharkiv, near the Russian border, have been intensifying in recent weeks.

It has suffered extensive damage in the two years of war.

Kharkiv a target for a new offensive 

Air defenses intercepted 28 out of 32 drones and three of six missiles fired by Russia, the military said.

Fighting along the approximately 1000-kilometer (620 miles) front line that stretches across the south and east Ukraine remains largely deadlocked.

Ukrainian President Volodymyr Zelenskyy has, however, warned Russia could attempt a new offensive in late May or early summer.

Zelenskyy's chief of staff, Andriy Yermak, told Politico in an interview published on Thursday that he saw Kharkiv as the most likely target for a new Russian offensive.

Attacks on Ukrainian civilian infrastructure

The attack on Kharkiv came a day after a Russian strike on the southern city of Zaporizhzhia killed four people and wounded more than 20. 

Ukraine's internal ministry Saturday updated the wounded toll in the Zaporizhzhia strike to 23, which included two children. 

The US think tank, the Institute for the Study of War (ISW), said this week the goal of Russia's escalated attacks on civilian areas and the country's power grid might be to compel Ukraine's army to deploy air defense systems away from the front line.

The think tank added that this would allow Russia to provide more air cover for its ground operations on the battlefield.

rm/lo (Reuters, AFP)