The decision left officials on both sides of the Atlantic scrambling to find out how long the pause might last.

The White House cited Pentagon concerns that some American arms stockpiles were dwindling too low. Among the affected weapons were air defense systems, bombs, missiles and artillery rounds.

The decision is a setback for Ukraine as it tries to fend off escalating attacks from Russia, which has deployed 50,000 troops near the border with Ukraine's Sumy region. President Donald Trump said he is watching the situation closely amid fears of a new offensive.