Russian strikes on the frontline town of Kupiansk in northeastern Ukraine left six people dead, regional officials said, piling pressure on a region where Moscow's forces have been on the offensive.

The updated toll in Kupiansk brought the total killed in Ukraine that day to nine people.

The attack in the northeastern region of Kharkiv near the border with Russia came after a swarm of attack drones destroyed warehouses and left one dead overnight in the western city of Lviv.

"The number of dead has increased to six people. Four men and two women were killed in Kupiansk as a result of an enemy attack from a guided aerial bomb," the regional governor, Oleg Synegubov, said on social media.

"Emergency services continue to work at the scene of the explosion," he added in a statement.

Russian forces captured swathes of the Kharkiv region early in the invasion launched in February 2022, but Ukrainian troops have since pushed back.

In the southern town of Kherson, a policeman died when a trolleybus was hit and two passengers were wounded, said Roman Mrochko, administration chief for the major southern city recaptured from the Russians last November.

One of the wounded, a 57-year-old man, died later from his injuries.

The governor of the Lviv region in the west, 1,000 kilometres (600 miles) from the frontlines and close to Poland, had earlier announced that one person was killed during a Russian drone attack in the night.

An AFP reporter in the area had heard the drones followed by explosions.

Seven of the drones were shot down but warehouses in Lviv were hit and a fire broke out, governor Maksym Kozytsky said on Telegram.

The body of a 32-year-old man was found in the remains of a burnt-out building while a 26-year-old was treated in hospital. A 68-year-old received medical care at the scene, the governor added.

A warehouse for the non-governmental organisation Caritas-Spes, which held 300 tonnes of emergency supplies, was "totally burnt-out," the United Nations Office for the Coordination of Humanitarian Affairs (OCHA) said.

OCHA Ukraine coordinator Denise Brown condemned the Russian strike.

"Attacks against humanitarian resources have intensified during the year with consequences for those who suffer the horrible consequences of the war," she said.

The Ukrainian army said 27 Iranian-made Shahed drones had been shot down out of 30 launched by Russia during the night.