Image copyright Reuters Image caption Protesters displaying caricatures of Joe Arpaio and Donald Trump gathered in Phoenix, Arizona

US President Donald Trump should not have pardoned a former Arizona sheriff who took a hard line on immigrants, the top Republican in Congress has said.

Paul Ryan, speaker of the House of Representatives, spoke out after Mr Trump pardoned Joe Arpaio, convicted last month of criminal contempt.

Mr Arpaio had defied a court order to stop traffic patrols that targeted immigrants suspected of being illegal.

President Trump tried to have the case dropped months ago, US media say.

He asked both Jeff Sessions, the attorney general, and Donald F McGahn II, the White House counsel, what the options were for helping Mr Arpaio, a longtime Trump supporter, the New York Times says, quoting unnamed officials.

Mr McGahn and Mr Sessions both promptly told the president the case could not be dropped and the charges wiped away, according to the officials, speaking anonymously.

"After talking with Sessions, Trump decided to let the case go to trial, and if Arpaio was convicted, he could grant clemency," a Washington Post story says.

'Diminished by this pardon'

"The speaker does not agree with the decision," Mr Ryan's spokesman, Doug Andres, said.

"Law-enforcement officials have a special responsibility to respect the rights of everyone in the United States. We should not allow anyone to believe that responsibility is diminished by this pardon."

Image copyright Reuters Image caption Mr Ryan is the latest senior politician to condemn the former policeman's release

Other prominent critics of the pardon from within Mr Trump's Republican Party include Arizona Senator John McCain and former Florida Governor Jeb Bush.

Arizona's other Republican senator, Jeff Flake, also condemned the move as did Democrats and human rights campaigners.

Mr Arpaio, 85, has described his conviction as "a witch hunt by the Obama justice department".

His lawyer, Jack Wilenchik, said those criticising his pardon were wrong because he had been unfairly prosecuted, with no jury.

Image copyright AFP Image caption Mr Arpaio, 85, has hinted that he may stand again for public office following his pardon

The pardon is unusual in several respects, according to an Associated Press analysis:

Mr Arpaio did not submit an application through the Office of the Pardon Attorney

His pardoning took place before he was sentenced (sentencing had been set for 5 October)

He was pardoned for a misdemeanour offence, which carries a penalty of less than a year in jail, when generally those seeking a presidential pardon have been convicted of felonies

The former sheriff was an eager supporter of Mr Trump's campaign to become president and backed tougher policies to combat illegal immigration.

In a statement announcing the pardon, Mr Trump said his life and career exemplified "selfless public service".

"Throughout his time as sheriff, Arpaio continued his life's work of protecting the public from the scourges of crime and illegal immigration," the president said.

The former policeman has said he may consider running for public office again, despite his age.