U.S. President Donald Trump has frozen military aid to Ukraine, just days after publicly confronting Ukrainian President Volodymyr Zelenskiy at the White House and accusing him of being insufficiently grateful for Washington's backing.

The U.S. move won’t have an immediate impact on the battlefield, where Kyiv’s forces are struggling to stem a relentless Russian offensive in eastern Ukraine. Ukrainian forces have slowed Russian advances along the roughly 1,000-kilometer (600-mile) front line, where Russia is slowly gaining ground at a huge human and material cost.

U.S. officials said the halt in military funding, an extraordinary pressure tactic, would be lifted if Ukraine’s president shows an openness to peace talks.