But now, former foreign minister Jaswant Singh stands accused of sparking a spy chase that has gripped India in a bid to boost sales of his just-released memoirs "A Call to Honour".

The book has launched India's media spycatchers on a hunt for the identity of a political "mole" who was supposedly in cahoots with the Americans and leaked word to Washington that India planned to declare itself a nuclear power in the 1990s.

"The Mole Controversy -- The Nuclear Nexus," said India's biggest-selling news magazine India Today after Singh's book was published in July. It is already in its fourth printing.

The mystery stems from a letter dated 1995 that Singh, who leads the main right-wing opposition party in the upper house of parliament, said was written by a US diplomat based in Delhi to a senator in Washington.

The letter said the nuclear information came from a "senior person" with "direct access" to then Congress prime minister P.V. Narasimha Rao.

It has triggered suspicion that a top-level bureaucrat or scientist may have been spying for the Americans.

Singh, 68, who helped steer India through the nuclear standoff with rival Pakistan four years ago as foreign minister in the former Hindu nationalist Bharatiya Janata Party (BJP) government, initially said he would reveal the name only to Congress Prime Minister Manmohan Singh.

But Singh, a former military man whose memoirs are peppered with references to decency and honour, has refused to "name names," saying, "I am actually not given to indecent exposure."

Pressure on him has been mounting and Singh has been backtracking. He now says he does not know the identity of the mole.

This earned him a stinging dressing down from the prime minister, who questioned his integrity, and calls for him to reveal the name in the interests of national security.

"If he has the decency and the courage, he should name the person whom he is accusing of being a mole," said the prime minister.

"You are levelling serious charges -- that we were being snooped (upon), he said in parliament.

Jaswant Singh alleges that the spy informed Washington about India's plan for a nuclear test in the mid-1990s. He says that subsequent American pressure forced India to postpone the test till 1998 when the BJP was in power.

The issue the book raises of Americans allegedly spying on India comes at a sensitive time.

Controversy has been growing over a deal with the United States to give India access to civil nuclear technology that critics say would give Washington too much leverage over New Delhi's security policy.

"The Indian who betrayed his country may be listening to his own heartbeats, but his identity is not the only issue that matters," said India Today editor Prabhu Chawla, whose news magazine splashed the story on its cover.

"Is the (Indian) current nuclear agenda independent of external influence? Has India (been) compromised?" he said.

On Thursday, a US embassy spokesman in New Delhi called the letter "a poor imitation" of official US correspondence."

A retired senior Indian intelligence official B. Raman also said he doubted its genuineness, noting it used British instead of US spellings.

However, he also alleged Rao's government planned to stage nuclear tests in 1995 and called them off due to US pressure. He said it was commonly believed Washington learnt of the plans "through satellite" images.

"There is a case for an inquiry into how the leakage (of information) occurred," he said, but added that the document cited by Singh had circulated for years and might have been written "by an Indian" to try to discredit Congress.

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