Phone calls from prison believed to have been made by the murderer of a much-loved shopkeeper will be investigated by police.

Tanveer Ahmed, 32, from Bradford, drove more than 200 miles to Glasgow to launch a brutal knife attack on Asad Shah, 40, in his shop in March of this year because he claimed to be a prophet.

Ahmed walked into the newsagents in the city's Shawland's area before confronting fellow Muslim Mr Shah, pulling a knife from his robes and repeatedly stabbing him in the head, punching and stamping on him.

Ahmed appeared at the High Court in Glasgow on Thursday, when he pleaded guilty to the religiously motivated murder of Mr Shah - an Ahmadi Muslim who are persecuted by other Muslims around the world.

Mr Shah was left with a broken jaw, broken nose and cheek bones. The assault was so severe that he also suffered a fractured skull to an extent more often seen in victims of car crashes.

Police are now probing phone calls believed to have been made by Ahmed while in Barlinnie prison after his arrest boasting about the murder and saying he would do it again.

A senior police chief has told STV News that the force "will commit resources" to investigating the calls.

In a phone call recording obtained by STV News and shared among supporters online, a man identified as Ahmed says: "To all Muslims, to the righteous, all Sunnis and all righteous scholars: I declare this on oath. The action, which I have taken, I have done to guard the honour of the Prophet.

"With reference to this, I have no regrets. I have sent a sinner to hell, a bad person to hell. I do not have any sympathy for his family or for him, nor do I have any regrets.

"I am on the side of right. I have no regret, no sympathy. I wont ask for forgiveness in the future, and I am not asking for it now. I am not worried about anything.

"I believe in God's mercy, and I have confidence in the kindness of the Almighty. I guarded with the help of God and His Prophet. I have no regrets, no worries, no afterthoughts. I am absolutely on the side of right and on the side of righteous people.

"I have done it to guard the honour of the Prophet and if I had to do it again in my life, I would."

Assistant chief constable Steve Johnson told STV News: "We are aware that there are communications that may have come from Barlinnie.

"That is something that we are going to have to look into and we will commit resources to make sure we look into that.

"When we get information to suggest that crimes have been committed or people have used communications from prison, we'll investigate those with a clear mind, with an objective mind to make sure that any offences are thoroughly investigated on behalf of the Crown and ourselves."