Pakistan's Supreme Court delayed an appeal into a notorious blasphemy case against a Christian mother on death row Thursday as one of the judges stepped down, with thousands of security forces deployed after threats from Muslim clerics.

Police and troops had been stationed across Islamabad as the court readied to hear a final appeal in the case of Asia Bibi, who has been on death row since 2010. Observers had warned of "tremendous" repercussions for minorities in deeply conservative Pakistan.

But one of the three-judge bench, Justice Iqbal Hameed ur Rehman, told the court he had to recuse himself, claiming a conflict of interest.

"I was a part of the bench that was hearing the case of Salmaan Taseer, and this case is related to that," he told the court.

Taseer, a liberal provincial governor, was gunned down in Islamabad in 2011 after speaking out for Bibi.

His assassin, Mumtaz Qadri, was hanged earlier in 2016 in a step liberals hailed as progressive, but which brought hardliners into the streets calling for Bibi's death.

Rehman was chief justice on the Islamabad High Court which heard Qadri's appeal in 2011, according to local media.

The Supreme Court did not immediately set a new date for Bibi's appeal. 

Blasphemy is a hugely sensitive issue in Pakistan. Anyone even accused of insulting Islam risks a violent and bloody death at the hands of vigilantes.

Rights groups complain the controversial legislation is often abused to carry out personal vendettas, mainly against Christians.

Observers had warned of possible violence if Bibi's conviction was overturned, with some calling the case a battle for Pakistan's soul as the state walks a line between upholding human rights and appeasing hardliners.

Clerics at the influential Red Mosque in Islamabad warned late Wednesday they would launch a nationwide protest if Bibi is released.

"Any one who will defend or will protect the blasphemer of the Prophet will equally be considered as blasphemer," spokesman Hafiz Ihtesham Ahmed said.

He warned against foreign diplomats lobbying for Bibi's release, saying clerics would mobilise the public if she was freed and "everyone will become Qadri".

Bibi's lawyer Saif-ul-Mulook called the Red Mosque threat "big".

"I hope the government takes it very seriously and takes care of our security," he told media outside the court Thursday.

- Judges 'apprehensive'? -

Zohra Yusuf, chair of the independent Human Rights Commission in Pakistan, told AFP the appeal delay was "regrettable", noting that Bibi was already being held in solitary confinement due to security concerns.

The judges may be "apprehensive", she said, adding that after the Supreme Court announced its decision to uphold Qadri's death sentence, justices had to sneak out the back door to the court.

"It's a sensitive case. I think they (the judges) have realised that if Asia Bibi (is) acquitted, they may be putting their own lives on the line," Yusuf said.

A senior police official told AFP that up to 3,000 security personnel had been deployed in the capital earlier Thursday.

Bibi was convicted and sentenced to hang in 2010 after an argument with a Muslim woman over a bowl of water. Her supporters maintain her innocence and insist it was a personal dispute, and the Vatican has called for her release.

But successive appeals have been rejected, and if the Supreme Court bench eventually upholds Bibi's conviction, her only recourse will be a direct appeal to the president for clemency.

If that fails, she could become the first person in Pakistan to be executed for blasphemy. 

The repercussions for minorities, human rights and the blasphemy laws would be "tremendous", says Shahzad Akbar, a human rights lawyer.

Source: AFP