Pakistani authorities have barred the family of a murdered social media celebrity from legally "forgiving" their son for strangling her, sources said, in a rare stand against the so-called practice of "honour killings".

Reuters reports that Muhammad Waseem drugged and strangled Qandeel Baloch on Friday in a murder that has shocked Pakistan, a deeply conservative Muslim nation where the 26-year-old both titillated and outraged with her risque; social media photos and videos.

Waseem told media he had "no regrets" about killing his sister as she violated the family's honour by her social media pictures, including "selfie" photographs with prominent Muslim cleric Abdul Qavi. In a video post with Qavi, she appears to sit on his lap.

A police source said the government of Punjab, the country's largest province, has made it impossible for the family to forgive the son who murdered her - a common legal loophole that sees many honour killings go unpunished in Pakistan.

"It was done on the instructions of the government. But it happens rarely," said the Punjab police official.

A senior government official in Islamabad confirmed the order came from the Punjab government.

More than 500 people, almost all of them women, die in honour killings in Pakistan every year, usually at the hands of relatives acting over a perception shame has been brought on the family.

It was not immediately clear if the Punjab government's decision would lead to any meaningful reforms. An anti-honour killings bill that aims to close the family forgiveness loophole has been bogged down in parliament.