Russian forces have blown up a bridge linking the embattled Ukrainian city of Sievierodonetsk to another city across the river, cutting off a possible evacuation route for civilians, local officials said on Sunday.

Sievierodonetsk has become the epicentre of the battle for control over Ukraine’s eastern region of Donbas. Parts of the city have been pulverised in some of the bloodiest fighting since the Kremlin unleashed its invasion on February 24.

Ukrainian and Russian forces were still fighting street-by-street there on Sunday, the governor of Luhansk province, Serhiy Gaidai, said.

Russian forces have taken most of the city but Ukrainian troops remain in control of an industrial area and chemical plant where hundreds of civilians are sheltering.

But the Russians had destroyed a bridge over the Siverskyi Donets river linking Sievierodonetsk with its twin city of Lysychansk, Gaidai said. That leaves just one of three bridges still standing, and reduces the number of routes that could be used to evacuate civilians or for Ukrainian troops to withdraw to positions on the western side of the river.

In Lysychansk itself, Russian shelling killed one woman and destroyed four houses and a shopping centre, Gaidai said.

The head of the Sievierodonetsk administration said a little more than a third of the city remained under the control of Ukrainian forces and about two-thirds were in Russian hands. “Our (forces) are holding the defensive line strongly,” Oleksandr Stryuk told national TV.

Moscow has turned its attention to expanding control in the Donbas, where pro-Russian separatists have held a swathe of territory since 2014. Sievierodonetsk is the last city in Donbas’s Luhansk province still held by Ukraine and its loss would be a significant strategic blow.

Elsewhere, Russian cruise missiles destroyed a large depot containing US and European weapons in western Ukraine’s Ternopil region, Russia’s Interfax agency reported.

Ternopil’s governor said rockets fired from the Black Sea at the city of Chortkiv had partly destroyed a military facility and injured 22 people. A local official said there were no weapons stored there.

Moscow has repeatedly criticised the US and other nations for supplying Ukraine with weapons. Russian President Vladimir Putin said earlier this month that Russia would strike new targets if the West supplied longer-range missiles to Ukraine for use in high-precision mobile rocket systems.

Ukrainian leaders have renewed pleas to western countries in recent days to speed up deliveries of heavy weapons as Russian artillery pounds the east of the country.

To the south and southwest of Sievierodonetsk, Russian forces were firing mortars and artillery around a number of settlements, according to Ukraine’s general staff. But it said Ukrainian forces had repulsed Russian attempts to advance towards some communities.

Ukrainian forces have proven more resilient than expected, but the US-based Institute for the Study of War said that as they use the last of their stocks of Soviet-era weapons and munitions, they would require consistent western support.

Nato backs Turkey

Security concerns raised by Turkey in its opposition to Finland’s and Sweden’s Nato membership applications are legitimate, Nato secretary-general Jens Stoltenberg said on Sunday during a visit to Finland.