Russian forces have almost completely surrounded Ukrainian troops in Russia’s Kursk region, with some Ukrainian units forced to leave their vehicles behind as they pull back, according to a U.S. military official.

Russian President Vladimir Putin has called on Ukrainian troops in the Russian region of Kursk to surrender, as diplomatic back-and-forth continues over a potential US-brokered ceasefire with Ukraine.

President Trump and President Vladimir V. Putin both claimed that Ukrainian forces were surrounded. Ukraine’s top military commander vowed to “hold the line.”