Lahore: Pakistani police on Monday arrested sister and cousin of Qandeel Baloch for their "possible involvement" in the murder of the social media celebrity who was killed by her brother for protecting the family's 'honour'.

"Shahnaz and Haq Nawaz, the sister and cousin of Qandeel, have been taken into custody for investigation in her murder case," an investigation officer told reporters.

Muhammad Waseem, brother of Qandeel, had killed the model on 16 July at their Multan residence, some 350 kilometres from Lahore, for for 'dishonouring' the family.

On Monday, a judicial magistrate extended the physical remand of Waseem into police custody for another three days for interrogation.

Waseem, in his confessional statement claimed to have acted alone and said he had drugged and strangled his sister in the name of honour.

Police, however, are looking to investigate Shahnaz and Haq Nawaz for their "possible involvement" in Qandeel's murder. Police have also conducted polygraph and DNA tests at Waseem.

Senior police officer Ali Mardan said police would also summon cleric Mufti Abdul Qavi this week for interrogation.

Qavi was embroiled in a controversy with Qandeel when she uploaded her pictures with him on her Facebook account. Qavi, who was suspended from the Ruet-e-Hilal Committee in the controversy following the video posts, has also been included in the murder inquiry by the police.

After Qandeel's murder, the PML-N government has announced enacting law to remove a loophole allowing other family members to pardon a killer.

Earlier, police said that Waseem had killed his sister for the "honour of the family".

The 'honour-killing' had sent shockwaves across the country and triggered an outpouring of grief on social media for Qandeel.