ISLAMABAD (AP) — A Pakistani court ruled Tuesday that the closed-door prison trial of former Prime Minister Imran Khan on charges of revealing state secrets is illegal, his lawyer said.

The ruling by the Islamabad High Court came on a petition filed by Khan, who has demanded an open trial, lawyer Naeem Haider Panjutha said.

It was unclear whether the government would appeal, or if future open court proceedings would take place at the same prison in the garrison city of Rawalpindi or somewhere else. Authorities have insisted Khan was being tried at Adiyala Prison because of threats to his life.

The court’s decision came about a month after Khan was indicated for allegedly revealing a secret document. Legal experts say the charges he faces carry a possible death sentence in the event of a conviction.

Khan’s close aide, Shah Mahmood Qureshi, who was deputy in his Pakistan Tehreek-e-Insaf party, is a co-defendant in the case. Both men have denied the charges them during the trial.

The case is related to Khan’s comments about and waving of a confidential diplomatic letter at a rally after his ouster in a no-confidence vote in parliament in 2022. He and Qureshi are accused of communicating information in the classified letter to unauthorized people for political gain.

The document — dubbed Cipher — has not been made public by either the government or Khan’s lawyers but was apparently diplomatic correspondence between the Pakistani ambassador to Washington and the Ministry of Foreign Affairs in Islamabad.

Khan claimed the document was proof that his ouster was a U.S. conspiracy, allegedly executed by the military and his political opponents, including his successor Shehbaz Sharif. Washington, Pakistan’s military and Sharif have denied the claim.

Khan has not appeared in public since August, when he was sentenced to three years for corruption. The Islamabad High Court subsequently suspended that sentence but he remained in custody due to his arrest in the Cipher case.

Tuesday’s development came ahead of the parliamentary elections which are to be held on February 8.

According to analysts, Khan’s party still could win the most seats, but he is not eligible to run for parliament due to his conviction in the graft case.

Also Tuesday, a court in Islamabad briefly heard an appeal from Khan’s main political rival, Nawaz Sharif, against his 2018 conviction in a graft case. Sharif, who served as prime minister three times, returned to Pakistan in October, ending four years of self-imposed exile in London mainly to lead his Pakistan Muslim League party in the parliamentary elections.

During his tenure, Khan allowed Sharif to travel abroad to receive medical treatment. But he prolonged his stay in London, saying his doctors would not allow him to return to Pakistan. Sharif returned home only after Khan was arrested and imprisoned.