Fighting between Russian and Ukrainian forces has reached the outer limits of the key eastern Ukrainian city of Severodonetsk, the governor of Luhansk said Wednesday, describing combat as "very difficult."

"Russian troops have advanced far enough that they can already fire mortars" on the city, Luhansk governor Serhiy Haidai said in a statement on social media, adding that "yesterday there was already fighting on the outskirts of the city."