India has warned Pakistan that any move to execute an Indian naval officer convicted by a Pakistani court-martial of spying would be "premeditated murder".

Sushma Swaraj, India's foreign minister, has also assured legislators that the government would go "out of its way" to save Kulbhushan Jadhav from the death sentenced handed out, according to Indian media reports.

On Monday, Pakistan's military sentenced Jadhav to death on charges of espionage and sabotage.

In a statement, the army said Jadhav, who was arrested in March 2016, was an Indian intelligence official "who aided and financed terrorist activities" in the southwestern Balochistan province and the southern port city of Karachi.

India's foreign ministry said it had summoned Abdul Basit, Pakistan's high commissioner, to lodge a protest following the statement released by Pakistan army.

It said there was no evidence against Jadhav, calling the proceedings against him "farcical".

In a letter issued to Basit and later released to the media, the foreign ministry said India's government had repeatedly sought consular access to Jadhav which was not permitted.

"If this sentence against an Indian citizen, awarded without observing basic norms of law and justice, is carried out, the government and people of India will regard it as a case of premeditated murder," said the letter.

Conflicting versions

Pakistan says Jadhav was arrested in Balochistan last year, but India alleges he was "kidnapped" in Iran.

Speaking at the upper house of the Indian parliament, Swaraj called Jadhav "a son of India" and issued a warning to Pakistan saying: "I would caution the Pakistani government to consider the consequences for our bilateral relationship if they proceed on this matter."

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"Our position is very clear, there is no evidence of wrongdoing by Kulbhushan Jadhav.

"This is an act of premeditated murder. He was doing a business in Iran and he was abducted and taken to Pakistan. We sought consular access, but were denied. He is innocent."

Pakistan accuses India of helping the separatist campaign in Balochistan, a charge denied by India.

India, for its part, says Pakistan aids separatist fighters in Kashmir, which has been divided between India and Pakistan since the end of British rule in 1947.

Both countries claim the Himalayan territory in full and have fought three wars over it.