Khan has been detained in a colonial era prison that lacked facilities like an attached bathroom and television and made it harder for family and friends to visit or send newspapers, books or food.

Khan was imprisoned on Aug 5 after being sentenced to three years jail for unlawfully selling state gifts during his tenure as prime minister from 2018 to 2022.

The uncertainty over whether Khan would be automatically released as a result of the High Court's decision is due to other court orders allowing for his arrest in other cases.

Islamist militants, who aim to overthrow the Pakistani government and install their own brand of strict Islamic law in the predominantly Muslim country of 220 million people, have been active in recent months.

Khan has been at the centre of political turmoil since he was ousted last year as prime minister in a no-confidence vote, raising concerns about Pakistan's stability as it grapples with an economic crisis.

Khan was barred from holding any public office for five years after he began a three year sentence on charges of unlawfully selling state gifts acquired by him and his family during his 2018-2022 tenure.

Khan initially alleged that his ouster from office in a parliamentary vote last year was backed by Washington and orchestrated by Pakistan's top generals.

It is a dramatic fall from the luxurious lifestyle that Khan, the charismatic cricketer-turned-politician, has along been associated with in Pakistan and abroad as a sporting icon and national hero.

Khan has been at the heart of political turmoil since he was ousted as prime minister in a vote of no confidence, raising concern about stability in the nuclear-armed country as it grapples with an economic crisis.

Khan was taken by police from his home in the eastern city of Lahore and transferred to Attock prison just outside Islamabad, where a court had convicted him of charges arising over the sale of state gifts.

Khan has faced a multitude of charges in different institutions and courts since his ouster, including graft, murder and sedition.

The case is related to diplomatic correspondence between Washington and Islamabad, which Khan said was part of a US conspiracy to topple his government.