KYIV (AFP, REUTERS) - Fighting between Russian and Ukrainian forces has reached the limits of the key eastern city of Severodonetsk, the regional governor said on Wednesday (May 25), describing the combat as “very difficult”.

“Russian troops have advanced far enough that they can already fire mortars” on the city, Luhansk governor Serhiy Gaidai said in a statement on social media, adding that “there was already fighting on the outskirts” on Tuesday.

The Russian military has plotted a steady course deeper into Ukraine’s eastern Donbas region since withdrawing its forces from the central and northern regions to consolidate efforts in the east.

Severodonetsk, with a pre-war population of around 100,000 people, has been under relentless Russian shelling for weeks, and is among key urban hubs in the industrial Donbas region on Russia’s list of military goals.

The other city in Moscow’s sights is Lysychansk, and Russian forces were advancing from three directions to encircle the cities.

“The coming week will be decisive,” Gaidai said, adding that he believes Russia’s goal is to “capture the Luhansk region no matter what cost”.

A representative of Moscow-backed separatist fighters – who have been in control of parts of Luhansk since 2014 – said that Severodonetsk was “operationally surrounded” by rebel troops and Russian forces.

“It’s only possible to exit from Severodonetsk via one bridge, which is also under the control of our firepower,” the separatist official told Russia’s Interfax news agency.

Meanwhile, President Vladimir Putin signed a decree on Wednesday simplifying the process for residents of Ukraine’s Russian-occupied Kherson and Zaporizhzhia regions to acquire Russian citizenship and passports.

The decree marks a further step towards the “Russification” of the two regions, where Moscow’s war in Ukraine has enabled it to establish a continuous land bridge linking Russia to the Crimean region that it seized from Ukraine in 2014.

Russia claimed full control of the Kherson region, north of Crimea, in mid-March, and holds parts of Zaporizhzhia region to the north-east.

In Kherson, the Ukrainian governor has been ousted and the military-civilian administration said earlier this month that it planned to ask Mr Putin to incorporate it into Russia by the year end. Kherson has seen an exodus of its residents.