A Russian breach on Ukraine’s eastern frontline has triggered a wave of indignation and confusion in Kyiv ahead of a crucial summit between Donald Trump and Vladimir Putin on Friday, in which the Russian president is expected to try to lock in battlefield gains.

Ukrainian and western military analysts said that Russian forces had advanced nearly 15km over the past few days along a narrow corridor parallel to Dobropillia, a coal mining town turned key logistical hub north of the stronghold of Pokrovsk that Russian troops have nearly encircled.

The shock advance threatens to cut off a vital road linking Dobropillia to Kramatorsk, the de facto capital of Ukrainian-held Donetsk region which the Russians aim to capture, while allowing the Kremlin’s forces to bypass and flank a belt of fortifications and defensive lines built in recent months.