Kulbhushan Sudhir Jadhav was arrested in 2016 in Pakistan's restive southwestern province of Balochistan -- a region where Islamabad has long accused New Delhi of backing separatist rebels.

He was sentenced to death by a closed Pakistani military tribunal in 2017, but the International Court of Justice ordered Islamabad last year to review the sentence, and he was later offered the right to appeal.

"Commander Jadhav refused to file a petition for the review and the reconsideration for his sentence and conviction," said attorney general official Ahmad Irfan.

"He instead preferred to follow up on his pending mercy petition", Irfan added.

He said Pakistan had written to the Indian high commission inviting it to file an appeal on Jadghav's behalf.

New Delhi maintains Jadhav retired from the navy in 2001 and was running a logistics business in Iran, where he was kidnapped and brought to Pakistan and forced to confess.

India and Pakistan routinely accuse one another of sending spies into their countries, and it is not uncommon for both nation to expel diplomats accused of espionage.

The fractious relationship between the neighbours has worsened since New Delhi expelled two Pakistan embassy officials over spying claims in late May.

New Delhi has also accused Islamabad of torturing two Indian diplomats arrested following an alleged hit-and-run in the Pakistani capital.

Tensions were already high after India in August scrapped Muslim-majority region Kashmir's semi-autonomous status and imposed a major security clampdown.