NEW YORK (NYTIMES) - United States President Donald Trump's admonition that police should not be "too nice" while transporting suspects drew laughter and cheers from a crowd of officers Friday (July 28), but police officials swiftly made it clear they did not find the words funny.

From New York to Los Angeles, law enforcement authorities criticised the president's remarks. Experts worried that his words could encourage the inappropriate use of force. A defence lawyer even signalled that he might use video of the speech in court.

The criticism online started shortly after Trump's comments, which came at an event in Brentwood, New York, which was intended to support police in their fight against La Mara Salvatrucha, or MS-13, a gang that has been accused of several killings on Long Island.

After calling for more immigration officers to help arrest the gang members, Trump told officers "please don't be too nice".

"Like when you guys put somebody in the car, and you're protecting their head, you know, the way you put your hand over" the head, he said, putting his hand above his head for emphasis.

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

The president's remark was denounced by police officials and organisations, including the International Association of Chiefs of Police, the Police Foundation and Steve Soboroff, one of the civilian commissioners who oversees the Los Angeles Police Department.

"What the president recommended would be out of policy in the Los Angeles Police Department," Soboroff told the Los Angeles Times. "It's not what policing is about today." The Suffolk County Police Department, in New York, which had officers at the speech, responded within two hours.

"As a department, we do not and will not tolerate roughing up of prisoners," it said on Twitter. The department "has strict rules & procedures relating to the handling of prisoners," the post said.

"Violations of those rules are treated extremely seriously."

The White House did not return messages seeking comment Saturday. Some supporters rallied to Trump's defence, including the police group Blue Lives Matter, which said on Twitter that the remark was obviously a joke.

A comment that garnered one of the biggest reactions came on Twitter after Ben Tobias, a spokesman for the police department in Gainesville, Florida, wrote that he disagreed with the president's remarks and that those who "cheered should be ashamed". By Saturday afternoon, his tweet had been liked nearly 230,000 times.