U.S. President Donald Trump took aim at London Mayor Sadiq Khan just minutes ahead of arriving at the U.K. for an official visit, calling him a “stone cold loser who should focus on crime in London, not me.”

Trump also said that Khan had been foolishly nasty to him as “by far the most important ally” of the U.K. In a second tweet, Trump went on to compare Khan to New York’s Mayor Bill de Blasio, who he called incompetent.

Trump had earlier slammed Khan before boarding the Air Force One bound for the U.K. and ruled out a meeting with the mayor because he didn’t think much of him.