North Korea has criticized South Korea for the latter’s purchase and ongoing deployment of American F-35 stealth fighter jets and threatened it will respond by developing and testing its own special weapons to destroy the aircraft.

North Korea’s warning comes as South Korea expressed hope that the recent summit between US President Donald Trump and North Korea’s Supreme Leader Kim Jong Un will help revive dialogue between the Koreas. Improved ties between the two countries, however, now look grim.

In a statement from North Korea’s state media, which was released on Thursday, an unnamed policy research director at the Institute of American Studies of North Korea’s Ministry of Foreign Affairs slammed South Korean authorities for talking about reconciliation and cooperation while acquiring more weapons from the United States.

“There is no room for doubt that the delivery of ‘F-35A’, which is also called an ‘invisible lethal weapon’, is aimed at securing military supremacy over the neighboring countries in the region and especially opening a ‘gate’ to invading the north in time of emergency on the Korean peninsula,” the policy research director said in a statement, according to Reuters.

South Korea approved a deal to acquire 40 F-35As from Lockheed Martin for $6.8 billion. South Korea announced the project in 2014 in a bid to cope with the then rising military threats from North Korea. 

The F-35 A have more sophisticated features, such as radar-evading capabilities and ability to perform ground-attack and air-superiority missions using a range of precision weapons. This gives the South significant advantage over the North’s fleet of ageing combat aircraft. 

Animosity between the South and the North has since eased but Seol pushed through with its purchase of the fighter jet. 

Military officials expect that by the end of 2021, all of the fighter jets will be deployed and combat-ready.  The first two of the aircrafts already arrived in March and two others are expected to arrive in the coming weeks.

On Thursday, North Korean authorities claimed the second batch of F-35s will arrive in South Korea in mid-July, albeit Seoul officials refused to confirm. 

The unnamed North Korean government researcher commented that South Korea’s purchase of the American jets was meant to please the United States despite it being an extremely dangerous action that can worsen military tensions.