Kim Jong Un has accused the U.S. and South Korea of carrying out nuclear military drills. In response to the claim,  Un conducted a test Sunday simulating a nuclear counter attack on the U.S. and South Korea.

These aren’t the first accusations made by Un. On Sunday, tensions escalated after Un launched short range ballistic missiles from North Korea as part of ongoing tests, he said. Those missiles traveled approximately 500 miles, according to reports from South Korea and Japan. Un then went one KCNA, the North Korean State media, telling reporters that the threat of a Nuclear attack on the U.S. and South Korea was likely.

Furthermore, Un claims that testing his short range ballistic missile, helped to improve North Korea’s military capability if there was a need for a counter-offensive in a time of war. He stated that he needed to guarantee the country’s readiness for any “immediate and overwhelming nuclear counterattack.”

Un also claimed that countries such as the U.S. and South Korea “are getting ever more pronounced in their moves for aggression against” his country, according to reports from Fox News. Un said that it is of urgent matter that North Korea needs strengthen its nuclear arsenal in the wake of aggression towards his country.

“The nuclear force of the DPRK will strongly deter, control and manage the enemy’s reckless moves and provocations with its high war readiness, and carry out its important mission without hesitation in case of any unwanted situation,” Kim was quoted as saying.

The Associated Press reported that Jeon Ha Gyu, spokesperson of South Korea’s Defense Ministry, said it’s clear North Korea with its ramped-up testing activity is making “considerable progress” in nuclear weapons technology. According to reports Gyu did not detail any findings on North Korea’s  claim about the successful warhead detonation.

Annual exercises have been carried out for week by the U.S. and South Korea which involve, U.S. B-1B strategic bombers. The B-1B bomber is capable of carrying up to 24 nuclear bombs and can travel at a speed of mach 0.9 while dropping bombs from 200ft above the ground. North Korea claims that these exercises are a very real threat to the country and that is is merely a rehearsal for what they believe to be a full on attack of their country.