Kim Jong Un has changed North Korea's constitution so its military is required to launch a retaliatory nuclear strike if the dictator is assassinated.

The move is said to have been prompted by the killing of Iran's supreme leader Ayatollah Ali Khamenei and several of his top advisers during the opening phase of the joint US-Israeli attacks on Tehran.

According to South Korea's National Intelligence Service (NIS), the constitutional revision was adopted during the first session of the 15th Supreme People's Assembly, which opened in Pyongyang on March 22.

The changes formalise procedures for a nuclear response in the event Kim is killed or left unable to command the country's armed forces.

Under the revised Article 3 of North Korea's nuclear policy law, a retaliatory nuclear strike would be launched 'automatically and immediately' if the country's nuclear command-and-control system is threatened by hostile attacks, according to the NIS briefing.

Analysts said the decision appeared to reflect deep concern within the regime after the success of the US and Israel's strikes targeting Iran's senior leadership.

Professor Andrei Lankov, an expert in North Korean studies at Kookmin University in Seoul, said Pyongyang would have closely studied the attacks on Tehran and viewed them as a stark warning. 

He said the North Korean regime was likely alarmed by the speed and precision with which Iran’s military and political leadership had reportedly been targeted. 

Experts believe the changes are designed to ensure North Korea could still carry out a devastating nuclear response even if Kim himself is eliminated during the opening moments of a war.

Kim is known to be deeply concerned about his personal security and is constantly surrounded by bodyguards.

The North Korean dictator avoids flying whenever possible and instead travels in a heavily armoured private train fitted with advanced security systems. 

 Any attempt to assassinate Kim would likely be significantly more difficult than the strikes carried out in Iran because of North Korea’s extreme isolation from the outside world. 

The country’s borders remain effectively sealed and the small number of foreign diplomats, aid workers and businesspeople allowed into the country are subjected to constant surveillance and tight restrictions.

Analysts also noted that the type of intelligence gathering reportedly used in Iran would be far harder to replicate inside North Korea because of its limited CCTV networks and tightly controlled domestic intranet. 

Professor Lankov said North Korea’s leadership was also likely worried about advances in satellite surveillance technology, which could potentially track military movements or identify the locations of senior officials during a conflict.

He added that if North Korea's leadership believed the regime faced destruction, military commanders responsible for launching nuclear weapons would almost certainly obey orders for retaliation.

According to Professor Lankov, any retaliatory strike would most likely be directed at the United States rather than South Korea, which he said posed little realistic threat of launching an attack on the North independently.

The reports came as North Korea also announced plans to deploy a new type of long-range artillery weapon close to the South Korean border. 

State media said Kim had visited a munitions factory this week to inspect production of a new 155mm self-propelled howitzer. 

The official Korean Central News Agency claimed the artillery system has a range of more than 37 miles and would begin deployment to frontline units later this year.

That range would place central Seoul and large parts of Gyeonggi province, South Korea’s most densely populated region, within striking distance.