Imran Khan.

Imran was convicted of graft in August and jailed for three years, with the election commission subsequently banning him from contesting polls scheduled for January 2024.

"Let it be known that there's a difference of day and night between the Imran of today and Imran who was imprisoned on Aug.5," he said in the first statement to be released on his behalf since he was jailed.

"Today I am stronger and fitter; spiritually, mentally and physically, than ever before," added the former international cricket superstar. The statement also appeared on Imran’s X account.

Imran said he has spent his time in jail reading the Holy Quran, adding that he has "adjusted well to prison conditions."

Since being ousted last year Imran has been tangled in a slew of legal cases he says are designed to stop him from contesting elections.

He was briefly detained in May, sparking nationwide protests that turned violent, with anger directed at the military for allegedly interfering in politics.

The establishment responded with a fierce crackdown — rounding up thousands of supporters and forcing almost the entire central leadership underground. Many have since abandoned the party.

Although Imran’s prison term for graft was overturned, he was kept in custody over a fresh arrest for leaking state documents, with his lawyers expecting he will be formally indicted next week. It is a far more serious entanglement than graft and could see him imprisoned for 14 years.

The case relates to a cable that Imran had touted as proof that he was ousted as part of a US conspiracy backed by the establishment, according to a report by the government's Federal Investigation Agency. The United States and the Pakistan military have denied the claim.

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

Imran’s primary opponent, three-time prime minister Nawaz Sharif, is scheduled to return to Pakistan next week to lead his party through elections, ending four years of self-imposed exile in London.

Nawaz was barred from contesting the last general elections, in 2018, which Imran won on a wave of popular support and an anti-corruption manifesto.

"Do not give up," Imran told his supporters in Thursday's statement. "Keep raising your voice against this unelected predatory group and their facilitators at every forum and keep demanding a fair and transparent election in the country."