ISLAMABAD - Rights groups and church leaders on Tuesday urged Pakistan to halt the imminent execution of a man for a murder committed in 1992, saying his conviction was flawed.

The plea for mercy for Aftab Bahadur Masih, who is due to be hanged on Wednesday, comes after another prisoner condemned to death in contentious circumstances was granted a last-minute reprieve.

According to the Justice Project Pakistan (JPP), a human rights law firm handling his case, Masih was only 15 when he was arrested over a murder in Lahore.

The JPP says he was convicted on the basis of a confession extracted through torture from his co-accused Ghulam Mustafa, along with another eyewitness, and both have since retracted their statements.

British anti-death penalty campaign group Reprieve said it was a "scandal" that Pakistan was planning to hang Masih.

"The execution of this innocent man, arrested as a child, should immediately be halted," Reprieve's Maya Foa said in a statement.

Church leaders also appealed for a reprieve for Masih, who is a Christian.

The Roman Catholic Bishop of Karachi, Joseph Coutts, has written to President Mamnoon Hussain asking for Masih's hanging to be delayed so his case can be investigated.

In a separate letter several other church leaders including Michael Nazir-Ali, the former Bishop of Rochester in Britain, also called for clemency.

"Mr Bahadur has now spent 23 years in prison - more than a life sentence - for a crime that the two witnesses on which his conviction rest now say he is innocent," the letter says.

"To execute Mr Bahadur in these circumstances would be to commit a grave injustice."