The U.S. is refusing to provide air defenses to back the "reassurance force” the U.K. and France are planning in a postwar Ukraine, people familiar with the matter said.

British Prime Minister Keir Starmer has insisted a U.S. so-called backstop is essential to deter Russia from breaching any future ceasefire deal. But European allies have concluded during discussions with their American counterparts that President Donald Trump won’t provide the guarantees they have sought to back the Europe-led ‘coalition of the willing,’ according to the people, who requested anonymity disclosing private discussions.

The U.K. government declined to comment. The White House didn’t immediately respond to a request for comment.