Japanese and foreign Twitter users were left scratching their heads Thursday after a tweet a day earlier by U.S. President Donald Trump made reference to the mysterious "covfefe."

Trump tweeted just after midnight in Washington on Wednesday: "Despite the constant negative press covfefe."

The tweet went viral instantly, becoming one the most popular posts of the divisive U.S. leader before it was deleted after nearly six hours online. Trump later cracked a joke at the post, tweeting around 6 a.m.: "Who can figure out the true meaning of 'covfefe' ??? Enjoy!"