THE HAGUE, Netherlands -- India on Monday accused Pakistan of breaching the rights of an alleged spy who was sentenced to death by a Pakistani military court, a case at the U.N.'s highest court that has exacerbated tensions between the longtime rivals.

Indian lawyer Harish Salve told judges at the International Court of Justice that Pakistan's claims of espionage and sabotage against Kulbhushan Jadhav have "always been strong on rhetoric and blurry on facts."

Jadhav was arrested by Pakistan in March 2016 after he allegedly entered the country from Iran. Pakistani officials say he has been linked to 1,345 deaths in acts of terrorism in Pakistan, making secret trips to the country from Iran.

He was convicted in Pakistan by a military tribunal and sentenced to death in April 2017. The U.N. court last year ordered Pakistan not to execute him pending the outcome of the case in The Hague.

Monday's hearings played out against a backdrop of already high tensions between the neighbours over a deadly attack last week when a militant in the disputed Kashmir region rammed an explosive-laden van into a paramilitary bus, killing at least 40 soldiers. It was the worst attack against Indian government forces in Kashmir's history.

Four Indian soldiers, two suspected militants and a civilian were killed Monday in a gunbattle in Kashmir.

As hearings opened Monday in the Great Hall of Justice in The Hague, Salve said that Jadhav's court martial "hopelessly fails to satisfy even minimum standards of due process and ... should be declared unlawful."

He urged judges to declare Jadhav's continued custody unlawful and "considering the trauma to which he has been subjected for over three years, it would be in the interests of justice, of making human rights a reality, to direct his release."

India says Pakistani authorities ignored repeated requests to grant Jadhav access to consular officials and let him choose his own lawyer for the trial.

Pakistan lawyers are to set out their case on Tuesday.

After Monday's hearing, a member of the Pakistan delegation told reporters outside the court said India had not answered key questions about the case in its presentation to judges.

"You will hear what we have to say about this tomorrow," said lawyer Khawar Qureshi. "Today, we are disappointed with India's position. They've said nothing new."

The court's judges will likely take months to issue a ruling and their decisions are final and legally binding.