Thousands of supporters of Pakistan's jailed ex-prime minister Imran Khan are marching to the capital Islamabad as they call for his release.

Concerns over the 73-year-old's health have grown louder in recent months. His family claims he has lost most of his vision in his right eye after prison authorities failed to take action.

The cricket star-turned-politician, who faces charges in more than 100 cases, was jailed for 17 years over corruption last year. Khan said all the cases against him are politically motivated.

Even behind bars, he remains a force in Pakistani politics, and demonstrations in support for him have led to deadly violence and crackdowns in the past.

Sunday's march, which began in Lakki Marwat, a city 275km away from Islamabad, had paused for the night and is expected to resume around midday local time on Monday.

Originally scheduled for last week, it was postponed to allow for talks between the government and Khan's Pakistan Tehreek-e-Insaf (PTI) party but the talks ended in a deadlock.

Khan, who faces charges ranging from leaking state secrets to selling state gifts, was first imprisoned in August 2023. His wife Bushra Bibi was jailed along with him last year.

Sohail Afridi, chief minister for Khyber Pakhtunkhwa province ruled by PTI, expects that the march will make its way to a town about 80km (50 miles) west of Islamabad by Thursday.

"[By then] this movement will have reached every corner of the country and every square will have become a centre of activity," he said on Sunday, urging the people to "play an active role in the political process".

Authorities in Islamabad have stacked up shipping containers to block key access routes to the capital city.

The PTI said talks with government failed because authorities rejected the party's request for access to Khan so that its leaders could consult him on national and political issues.

The party also said it had demanded that Khan be given an immediate medical examination and treatment.

Interior Minister Mohsin Naqvi meanwhile accused Afridi of "sabotaging" negotiations, saying the Khyber Pakhtunkhwa government had backed out of earlier commitments on counter-terrorism issues, according to Pakistan's local media reports.

In August, Khan was briefly transferred from jail to a state-run hospital for medical examination and treatment following complaints about his deteriorating health. The doctors later deemed him "medically fit".

The intervention was the most significant relief Khan has received from the courts since he was imprisoned in 2023 on corruption charges, which he says were politically motivated.

Khan's family and the PTI, however, criticised the authorities for defying a court order that he be examined by physicians at a specific private hospital.

On 20 September, Khan's sister Aleema Khanum was arrested in the eastern city of Lahore.

The arrest order said Khanum had been mobilising people to "create law and order situations" and "raising/chanting objectionable slogans amongst the general public against the Government".

Khan, who previously captained the Pakistan national cricket team, served as the country's prime minister from 2018 to 2022.

His arrest in May 2023 sparked large-scale, violent protests by supporters, who ransacked the corps commander's residence in Lahore, smashing chandeliers and making away with furniture, paintings, and even peacocks, among other things.

At least eight people died in the protests and the army had to be called in to quell the violence.

Former international cricket captains have made several appeals in recent months to Pakistan's Prime Minister Shehbaz Sharif urging Khan be accorded proper medical care.