The Indian army says it is looking into allegations that an Indian brigadier sold its war plans to Pakistan during the Kashmir conflict in 1965.
Gohar Ayub Khan made his allegations in a Pakistan newspaper
Gohar Ayub Khan, son of an-ex Pakistan president, said on Monday the brigadier was paid 20,000 rupees (now $335).
Mr Khan did not reveal the brigadier's name but said he was still alive. He said the officer wanted to fund his wife's hobby for canning vegetables.
But on Wednesday an ex-Pakistan army chief said it received no such plans.
Mr Khan, a former Pakistan assembly speaker, made his allegations in an interview with Pakistani newspaper, The News, on Monday in the run-up to the publication of his autobiography.
He said he would give clear indications in his book to expose the officer's identity.
Mr Khan said the officer had now retired after achieving a high position in the Indian army.
Indian army chief Gen JJ Singh, said on Wednesday: "The army is doing an in-house verification on whether there is any truth in the allegation.
The 1965 war was the countries' second over Kashmir
"It is not correct to jump to conclusions or to speculate on a matter like this."
Indian Defence Minister Pranab Mukherjee has also announced a government investigation, but said: "I am afraid it is difficult to believe that an Indian brigadier would divulge military secrets for money.
"The way the news item has come up will require detailed analysis. Not to speak of a brigadier, nobody would have the detailed implementation plan."
Echoing Mr Mukherjee, one Pakistani general told The News: "It is almost inconceivable that a brigadier alone had complete knowledge of the detailed secret plan of the Indian army to attack Pakistan in 1965."
The newspaper said senior Pakistani army figures believed the disclosure could be a "publicity stunt" ahead of the autobiography's publication.
Former Pakistan army chief, Gen Mirza Aslam Baig, told an Indian television channel the 20,000-rupee figures was too small to be believed.
"For a secret war plan, the amount should have been 20 lakh rupees (2m)."
Gen Baig said the Pakistani army had received no such war plans from India.
"The only information that we got was from a dispatch rider from Jammu that the Indian army would launch its main offensive from the Rabi and Chenab region. It was a very small plan."
In his allegations, Mr Khan said Pakistani agents exploited the brigadier through his desire to satisfy his wife's whims.
Thousands of troops died in the 1965 conflict, which ended in a stalemate and a UN-mandated ceasefire.