Jailed former Pakistan prime minister Imran Khan was indicted on Monday for allegedly leaking classified documents, a charge set to keep him in custody in the countdown to national elections due early next year.

Since being ousted in 2022, Khan has been tangled in a slew of legal cases he says are designed to stop him from contesting polls in January, while his party has faced a massive crackdown.

A spokesman for Khan's Pakistan Tehreek-e-Insaf (PTI) party said he was charged under the colonial-era Official Secrets Act in a trial "conducted within the court premises with no access to public or media". 

The case relates to a diplomatic cable the 71-year-old allegedly touted as proof of a "conspiracy" behind the no-confidence vote which turfed him out of office last April.

"We are going to challenge it," Khan's lawyer Umar Khan Niazi told reporters outside the jail where the special court was convened.

Khan's lawyers say the crime he has been charged with carries a possible 14-year prison term, and in the most extreme circumstances, the death penalty.

Army courts stood down

Pakistan's supreme court gave rare respite to PTI on Monday by ordering that more than 100 supporters accused of rioting in May should not be prosecuted in military tribunals as planned.

"Under the Supreme Court verdict all the cases, which were being tried in the military courts, cannot be proceeded. They could only be held in the civilian courts," PTI lawyer Aitzaz Ahsan told reporters. 

"Today's verdict is highly significant and it will help strengthen the constitution, law, and the civilian institutions of the country."

The violence erupted after Khan was briefly arrested, with unprecedented anger aimed at the military. He was later convicted of graft in August and sentenced to three years in prison.

That sentence was overturned but he was kept in custody on the far more serious charge of sharing state documents he alleged proved how the army conspired with US diplomats to end his premiership.

The United States and Pakistan's military have denied the claim.

"PTI has been bled to death. The current army chief doesn't want it around, if it is around, it's minus Imran Khan," political analyst Ayesha Siddiqa told AFP.

"There is an entire movement out there by the establishment to eliminate him politically, at least for now," she said.

The vice-chairman of Khan's Pakistan Tehreek-e-Insaf (PTI) party, Shah Mahmood Qureshi, a former foreign minister, was also indicted over the same case.

Khan tangled up

Former cricketing superstar Khan enjoys enormous support in Pakistan but his street power has been squashed by the crackdown, which has seen thousands detained.

Almost the entire senior party leadership was forced underground, with many abandoning PTI.

On Sunday, PTI said about 80 members were rounded up at a convention in Lahore that they reportedly did not have permission for.

Pakistan's military has directly ruled the country for roughly half of its 76-year history, and continues to exercise enormous power.

The nation is currently led by an interim government, with polls already pushed back several months. 

Khan's primary opponent, three-time prime minister Nawaz Sharif, returned to Pakistan on Saturday, ending four years of self-imposed exile.

Sharif was jailed for graft and barred from contesting the 2018 elections - in which Khan swept to power - but he left midway through his sentence to receive medical care in the United Kingdom, ignoring court orders to return.

Prior to his comeback, a court granted Sharif protective bail in what analysts said was likely a backroom deal arranged by the army establishment.

The fortunes of Pakistan's leaders rise and fall on their relationship with the military and Pakistan's courts are often used to tie up lawmakers in lengthy proceedings that rights monitors criticise for stifling dissent.