Former Pakistani premier Nawaz Sharif, jailed earlier this month over graft charges, has fallen sick inside prison and is being moved to hospital, a minister said Sunday.

Sharif and his daughter were jailed on July 13 after a graft court sentenced them to 10 and seven years respectively over properties in Britain which emerged in the wake of Panama Papers revelations.

Caretaker home minister for Punjab province Shaukat Javed said on state-run Pakistan Television that doctors had advised his transfer to hospital after an electrocardiogram had shown "variations".

"How many days he stays in hospital depends on doctors," Javed said, adding that the former PM was being transferred to the Pakistan Institute of Medical Sciences in Islamabad.

Last week, the former PM was suffering from dehydration and his blood urea content was 50 per cent higher than it should have been. A medical team also recommended that he be shifted to the hospital as his heart beat was not normal and the presence of urea in the blood may affect his kidney.

However, Nawaz refused to be moved to a hospital and insisted that medical treatment be provided to him in prison.

Sharif, who claims he is being targeted by the country's powerful security establishment, is fighting for his political life after his Pakistan Muslim League-Nawaz (PML-N) party lost an election on Wednesday to rival Pakistan Tehreek-e-Insaf led by former cricket hero Imran Khan.

His brother Shahbaz, who heads the party now, has rejected election results along with other parties who have demanded fresh elections and announced they would protest against alleged election rigging.

The protests announcement late Friday came as the United States, the European Union and other observers aired reservations over widespread claims that the powerful military had tried to fix the playing field in Khan's favour.

Khan's victory represents an end to decades of rotating leadership between the PML-N and the Bhutto dynasty's Pakistan Peoples Party that was punctuated by periods of military rule.