Confidential Ukrainian assessments obtained by The Washington Post show how accuracy rates of some Western weapons fell after Russian jamming disrupted guidance systems.

Russia launched an offensive in the Kharkiv region late last week, significantly adding to the pressure on Ukraine’s outnumbered and outgunned forces which are waiting for delayed deliveries of crucial weapons.

Visiting U.S. Secretary of State Antony Blinken sought to reassure Ukraine of continuing American support, announcing a $2 billion arms deal, most of it from a package approved last month.

By Sunday afternoon, the town of Vovchansk, with a prewar population of 17,000, emerged as a focal point in the battle.

Russia’s recent push in Kharkiv also seeks to exploit ammunition shortages before promised Western supplies can reach the front lin, and pin down Ukrainian forces in the northeast.

The Ukrainian president warned on Thursday that his country was facing ‘a really difficult situation’ in the east.