Russia is reportedly massing approximately 50,000 troops, including significant numbers of North Korean soldiers, near Ukraine’s Sumy region for a potential summer offensive aimed at creating a “buffer zone.

The warnings over the offensive come as a U.S.-brokered peace process has limped along with inconclusive meetings and little concrete results.

Moscow’s dual campaign of intensified frontline attacks and bombardment of Ukrainian cities has further reduced the prospects for an end to the fighting.