Human rights campaigners, activists and police have raised concern over Donald Trump's apparent endorsement of police brutality, at a time when officers in the United States are under scrutiny for their use of excessive force.
The president on Friday advocated rougher treatment of people in custody while delivering a speech on gang violence and illegal immigration.
Trump told police officers from the Suffolk County Police department in New York on Friday to "not be too nice" when dealing with suspects.
He said his administration was targeting gang members, "but we'd like to get them out a lot faster".
"Please don't be too nice," he said, advising officers to use force when guiding "thugs into the back of a paddy wagon".
Trump then spoke dismissively of the practice by which arresting officers shield the heads of handcuffed suspects as they are placed in police cars.
"You could take the hand away," he said to an audience of federal and law enforcement personnel from the New York-New Jersey area, many of whom applauded Trump's remarks.
But the Suffolk County Police Department distanced itself from the president hours after his speech.
In a statement, the department said that it has strict rules and procedures about how prisoners should be handled.
"Violations of those rules and procedures are treated extremely seriously. As a department, we do not and will not tolerate roughing up of prisoners," the statement said.
Barbara Arnwine, president of the Transformative Justice Coalition, a Washington, DC-based civil liberties group, said Trump's remarks will encourage "bad cops and bad police divisions" to get involved in "roughing up" suspects.
"I think he is doing our nation a disservice by encouraging police departments to engage in unlawful, unconstitutional behaviour," she told Al Jazeera. "He is actually placing people's lives in danger."
Arnwine explained that in the moment someone is arrested, there are no formal charges or convictions against them.
"When a police officer takes someone into custody, you have no idea if they are guilty or not and it is illegal and unlawful for police officers to try to administer punishment when there have been no formal charges filed, no conviction, no sentencing," she said. "A punishment is specified by courts, not by police."
US police killed more than 1,000 people last year, almost 300 of whom were black, according to The Counted, a tracker by The Guardian.
Another monitor, Mapping Police Violence, claims that police have killed at least 160 black people so far this year.
Gray had been in police custody for allegedly carrying a switchblade in the US city of Baltimore.
He suffered a severe neck injury after his arrest, apparently while being transported in the back of a police van.
He complained about breathing difficulties, fell into a coma, and died one week later.
Arnwine said by not securing people in police custody, there could be more deaths like Gray's.
"What the president is advocating would lead to more deaths, more illegal police behaviour, police brutality," she said.
Rights groups American Civil Liberties Union (ACLU) also condemned Trump's speech.
"By encouraging police to dole out extra pain at will, the president is urging a kind of lawlessness that already imperils the health and lives of people of colour at shameful rates," said Jeffery Robinson, ACLU's deputy legal director.
Many took to social media to express their anger: