The trial proceedings that led to the capital punishment for Jadhav were also described by India as "farcical".
The award of the death sentence to the 46-year-old former Naval officer at a court-martial was confirmed by Pakistan's army chief Gen Qamar Javed Bajwa today and is expected to further deteriorate already strained Indo-Pak ties that were hit after the deadly attacks in Pathankot and Uri by Pakistan- based terrorists last year.
The court martial was closed to the public and consular access was not provided to Jadhav.
"The spy was tried through Field General Court Martial (FGCM) under the Pakistan Army Act (PAA) and awarded the death sentence. Today Chief of Army Staff Gen Qamar Javed Bajwa confirmed his death sentence awarded by FGCM," it said.
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Reacting strongly, Foreign Secretary S Jaishankar in New Delhi summoned Pakistan High Commissioner to India Abdul Basit and gave a demarche, which said the proceedings that have led to the sentence against Jadhav are "farcical in the absence of any credible evidence" against him.
Pakistan claims its security forces had arrested Jadhav from the restive Balochistan province on March 3 last year after he reportedly entered from Iran. It also claimed that he was "a serving officer in the Indian Navy."
The Pakistan Army had also released a "confessional video" of Jadhav after his arrest.
India had acknowledged that Jadhav had served with the navy but denied that he has any connection with the government.
India, through its High Commission in Islamabad, has repeatedly sought consular access to him, as provided for by international law and 13 such requests were formally made between 25 March 2016 and 31 March 2017, the demarche said.
The proceedings that have led to the sentence against Jadhav are "farcical in the absence of any credible evidence" against him, it said, adding it is significant that Indian High Commission was not even informed that Jadhav was being brought to trial.
According to the ISPR statement, Jadhav, a commander in the Indian Navy, "confessed" before a Magistrate and the court that he was "tasked by RAW to plan, coordinate and organise espionage/sabotage activities aiming to destabilise and wage war against Pakistan by impeding the efforts of Law Enforcement Agencies for restoring peace in Balochistan and Karachi."
"Senior Pakistani figures have themselves cast doubt about the adequacy of evidence. The claim in the ISPR release that Jadhav was provided with a defending officer during the so-called trial is clearly absurd in the circumstances.
"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," the foreign secretary said in the demarche.
India and Pakistan have been at loggerheads over several issues, including on Islamabad's support to terrorism, since the terror attack on an Indian army base in Uri in Kashmir in September last year by Pakistan-based militants killed 18 Indian soldiers.
The two sides were also engaged in a war of words last year over Pakistan's provocative statements on the turmoil in Kashmir following the killing of Hizbul Mujahideen commander Burhan Wani in July last year.