U.S. National Security Adviser John Bolton said on Saturday the Democratic People's Republic of Korea's recent missile launches violated a UN Security Council resolution and urged its leader Kim Jong Un to return to denuclearization talks.

It was the first time a senior U.S. official has described the tests as a violation of UN resolutions aimed at halting DPRK's nuclear and missile programs and came ahead of a four-day visit to Japan by U.S. President Donald Trump, who arrives later in the day.

"The UN resolution prohibits the launch of any ballistic missiles," Bolton said at a press roundtable. North Korea's (DPRK) test firings included short-range ballistic missiles and so there was "no doubt" it was a violation, he added.

Earlier this month, Kim Jong Un oversaw the first flight of a previously untested weapon – a relatively small, fast missile experts believe will be easier to hide, launch and maneuver in flight.

Bolton said that President Trump was still open to talks with Kim but that the administration had not changed its position from the one outlined at the last summit between the United States and DPRK in Hanoi.

But on Friday, the DPRK side reiterated that it won't resume talks with the U.S. unless it changes a "new method of calculation," Yonhap reported citing DPRK's state media Korean Central News Agency.

The Foreign Ministry spokesperson said the U.S. is attempting to shift the blame onto Pyongyang for the deadlocked situation.

"Unless the United States puts aside the current method of calculation and comes forward with a new method of calculation, the DPRK-U.S. dialogue will never be resumed and by extension, the prospect for resolving the nuclear issue will be much gloomy," the spokesperson said. 

(Cover: U.S. National Security Adviser John Bolton speaks during a graduation ceremony at the U.S. Coast Guard Academy in New London, Connecticut, U.S., May 22, 2019. /Reuters Photo) 

(With input from Reuters)