Image copyright Getty Images Image caption Some reports spoke of a grenade but police said it was a detonator

A device being presented as evidence at a trial in a Pakistani court blew up after the judge asked a police officer to show how it worked.

At least two people were injured, including the policeman, in the blast at an anti-terrorism court in the city of Karachi.

Some reports say the device was a grenade taken from the defendant.

Police later said it was just a detonator with an explosive element that should have been defused.

The incident took place on Monday at the trial of a man accused of extortion and of carrying out a number of grenade attacks.

Police said several devices had been found when they arrested him.

The device presented in court was at the request of the defence. Judge Shakil Haider then asked how it worked.

A part of the device was pulled from it and it exploded, throwing the judge off his chair.

Senior police official Jamil Ahmed said that explosives around the detonator had been made harmless, but added: "We are investigating as to how the detonator was brought to the court without being defused."