NEW DELHI (AFP) - India on Thursday (July 18) demanded that Pakistan release an alleged spy after the International Court of Justice (ICJ) called for a review of the death sentence imposed on him.

The arch-rivals each declared victory after the world court ruling made late on Wednesday.

But with 49-year-old Kulbhushan Jadhav still held incommunicado, his case risked setting off new tensions between the nuclear-armed neighbours.

India's Foreign Minister Subrahmanyam Jaishankar said Mr Jadhav, a former navy officer, "is in the illegal custody of Pakistan under fabricated charges" as he welcomed the court ruling.

"Yesterday's judgment is not only a vindication of India and Mr Jadhav, but (also) for all those who believe in the rule of law and the sanctity of international conventions," the minister added.

Mr Jaishankar insisted that Mr Jadhav "is innocent of the charges levelled against him" and had been forced to confess without access to a lawyer.

"We once again call upon Pakistan to release and repatriate him forthwith."

The ICJ said Pakistan must give India consular access to the prisoner, give Mr Jadhav proper representation, and review the death sentence. But it rejected India's demand that Mr Jadhav be freed.

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Pakistan said Mr Jadhav was detained in its south-western province of Baluchistan in March 2016.

It released a "confession" video in which Mr Jadhav said he worked for Indian intelligence. A military court sentenced him to death in 2017.

According to Indian officials, Mr Jadhav retired from the navy in 2001 and was running a logistics business in the Iranian port of Chabahar.

India insisted he was taken captive in Iran before being moved to Pakistan and then forced to confess.

It started an ICJ case in 2017.

Throughout the hearings, Mr Jadhav was kept under strict lock and key in Pakistan.

Apart from the video in which he said he graduated from India's premier defence academy and began to help Indian intelligence in 2001, the only sighting of him was when his mother and wife saw him for 40 minutes on Dec 25, 2017.

Indian officials say relatives reported that he appeared to have been tortured.

Relations between the neighbours frequently boil over. They have fought three wars since independence in 1947 and staged air battles on their border in February.

New Delhi frequently says there can be no improvement in relations until its neighbour takes action to rein in militant attacks in India.

Keeping up the rivalry, India's Prime Minister Narendra Modi said late on Wednesday that "truth and justice have prevailed" with the ICJ ruling.

His Pakistani counterpart Imran Khan hit back through his Twitter account.

"Appreciate ICJ's decision not to acquit, release and return Commander Kulbhushan Jadhav to India," Mr Khan said.

"He is guilty of crimes against the people of Pakistan. Pakistan shall proceed further as per law," he added.

Pakistan's foreign ministry said the incident is a "clear case of Indian state terrorism".

Media in the two countries also claimed victory in the case.

"India Wins in World Court," said a Mail Today headline.

"Justice in International Court," declared The Indian Express.

"Pakistan vindicated" ran a banner front-page headline in Pakistan's Express Tribune.