A lawyer has been arrested for allegedly giving a pistol to a teenager accused of gunning down a US citizen as he appeared in a Peshawar court on blasphemy charges, officials told AFP on Wednesday.

Last month's killing of Tahir Ahmad Naseem in a crowded courtroom sparked outrage in the United States.

The US State Department has urged Pakistan to take action in his case and called for a reform of the blasphemy laws under which he was being held.

Naseem, a US citizen of Pakistani origin, was under police escort when he was fatally shot in court on July 29.

According to investigating officer Lalzada Khan, a junior lawyer was arrested on Tuesday for “allegedly providing a pistol to the assassin to kill Naseem”.

“[The lawyer] was produced before the judge in an anti-terrorism court. He was remanded into police custody for three days,” Khan told AFP.

Authorities say the shooter, who according to police is 17 years old, has confessed to the killing, claiming the lawyer provided him with the pistol.

The teenager withdrew his bail petition from an anti-terrorism court on Monday, with a panel of lawyers telling the court that their client didn’t want to pursue the bail plea and was only interested in an early trial of the case.

Lawyers don't typically undergo a pat-down before going into courts, and officials said the arrested lawyer had discreetly handed the pistol over to the teenager.

Washington has said Naseem was lured from his home in Illinois to Pakistan in 2018, when he was arrested on blasphemy charges.

Up to 80 people are known to be imprisoned in Pakistan on blasphemy charges — half of whom face life in prison or the death penalty — according to the US Commission on International Religious Freedom.

The US State Department has put Pakistan on a blacklist over religious freedom, pointing to the blasphemy cases.