The U.S. President Donald Trump appeared to advocate rougher treatment of people in police custody during a speech in New York.

Speaking to police and crime victims in Brentwood, Long Island on Friday, the Trump suggested that officers are too careful in their treatment of people in custody.

Trump spoke dismissively of arresting officers who protect suspects' heads while putting them in police cars, saying "You can take the hand off." The line drew cheers from his audience.

"And when you see these thugs being thrown into the back of a paddy just see 'em thrown in, rough," he said

"I said, 'Please don't be too nice.' Like when you guys put somebody in the car and you're protecting the head. You know? The way you put the hand over [the head], like 'Don't hit their head' and they've just killed somebody, 'Don't hit their head.'

"I said, 'You can take the hand away,' OK?"

Trump also claimed that laws were written to "protect the criminal" and "not the officers," telling law enforcement officials among the crowd that the "laws are stacked against" them and needed to be changed.

The president then pledged to "destroy" the violent MS-13 street gang and other similar organizations.

He said he was more focused on MS-13 because it is "particularly violent," adding that MS-13's members don't like to shoot their victims because death comes too fast. He said MS-13 members preferred to knife and cut their victims, so they die slowly and more painfully.

"These are animals."

MS-13, or Mara Salvatrucha, committed a string of gruesome murders in Brentwood, New York, including the April killing of four young men.