Pakistan's jailed former prime minister Imran Khan has been charged with leaking classified documents, a prosecutor of the Asian nation has said.

"He has been indicted today and the charge was openly read out," said Shah Khawar of Pakistan's Federal Investigation Agency on Monday outside Adiala Jail where Khan is being held.

The ex-cricketing superstar was jailed in August for three years over graft but when his sentence was later overturned, he was instead kept in custody on the far more serious charge of sharing state documents.

Ex-foreign minister also indicted

The case relates to a cable that Khan had touted as proof that he was ousted as part of a US conspiracy backed by the powerful military establishment, according to a report by the government's Federal Investigation Agency.

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

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

Lawyers for Khan say the case carries a maximum jail term of 14 years.