Islamabad claims Mr Jadhav, a 46-year-old retired Indian Navy officer, was captured allegedly in Balochistan in March, 2016 by Pakistani security forces. India says he was kidnapped from Iran, where he went for business reasons. Mr Jadhav was tried in a military court in Pakistan, which has sentenced him to death for alleged "espionage and subversive activities".
The ICJ had asked Pakistan to submit its written response or memorial by December 13 before the court could start further proceedings.
According to Pakistan Foreign Office sources, Attorney General Ashtar Ausaf Ali yesterday presided over a meeting of law experts and officials of the ministry of foreign affairs and other relevant departments to discuss the line of arguments in the ICJ.
"We will forcefully defend our position which is based on the fact that Jadhav is a serving Indian spy tasked to carry out subversive activities in Pakistan," the Pakistani source alleged.
Meanwhile, Mr Ausaf told Pakistani newspaper Dawn that they had decided to hold weekly meetings in order to review the situation and "to finalise Islamabad's point of view and convert it into an appropriate rejoinder" to India's stand.
He said they were in touch with relevant stakeholders, including Khawar Qureshi who had pleaded Pakistan's case at the initial stage, to formalise a robust reply refuting all statements made by India.
The Pakistani daily reported that the attorney general's office is also busy documenting the case.
On Thursday, the Pakistan Army said it is close to a decision on the mercy petition of Kulbhushan Jadhav.
"Kulbhushan Jadhav's mercy petition has come to the army chief. There is a process, everything goes through a process but I can assure that it is near finalisation and we will give you news about this very soon," army spokesman Major General Asif Ghafoor said.
Mr Jadhav's death sentence was confirmed by Pakistan's army chief General Qamar Bajwa on April 10. He has filed an appeal with the army chief to seek clemency, which is still pending.
After India approached the ICJ, a 10-member bench on May 18 restrained Pakistan from executing Mr Jadhav till adjudication of the case.
Mr Jadhav's sentencing had evoked a sharp reaction in India. New Delhi has warned Islamabad of consequences and damage to bilateral ties if the "premeditated murder" was carried out.
In its application, India had also informed the ICJ that it learnt about the death sentence against Mr Jadhav from a press release. India has also handed over to Pakistan an appeal by Mr Jadhav's mother, initiating a process to get his conviction overturned.