President Donald Trump has appointed General John Kelly as his new White House chief of staff in place of Reince Priebus.
Mr Trump tweeted: "I am pleased to inform you that I have just named General/Secretary John F Kelly as White House Chief of Staff. He is a Great American."
Mr Kelly is currently the secretary of homeland security and Mr Trump tweeted that he "has been a true star of my administration".
Mr Priebus travelled with Mr Trump earlier in the day to an appearance in Brentwood, New York, and the president thanked him for his service and "dedication to his country".
Earlier today, President Trump has appeared to advocate rougher treatment of people in police custody during a speech in New York.
Mr Trump spoke dismissively of arresting officers who protect suspects' heads while putting them in police cars in a speech in front of law enforcement officials on Long Island.
He said: "You can take the hand off," drawing cheers from his audience.
He also claimed that laws are written to "protect the criminal" and "not the officers".
He told the law enforcement officials that the "laws are stacked against you" and need to be changed.
The president also pledged to "destroy" the violent MS-13 street gang and other similar organisations.
He said he is more focused on MS-13 because it is "particularly violent", saying MS-13's members do not like to shoot their victims because death comes too fast.
MS-13 members prefer to knife and cut their victims, so they die slowly and more painfully, he said. "These are animals."
The president addressed law enforcement officials and relatives of crime victims in Brentwood, in Suffolk County, New York, where MS-13, or Mara Salvatrucha, has committed a string of gruesome murders, including the April killing of four young men.