FILE PHOTO: North Korean leader Kim Jong Un waves to people attending a military parade marking the 105th birth anniversary of country's founding father, Kim Il Sung in Pyongyang, April 15, 2017. REUTERS/Damir Sagolj/File Photo

BEIJING (Reuters) - North Korea, increasingly isolated over its repeated weapons tests in violation of UN resolutions, on Monday renewed its accusation of a U.S. and South Korean intelligence plot to assassinate leader Kim Jong Un.

At a media briefing at its embassy in Beijing, North Korea’s ambassador to China said the U.S. Central Intelligence Agency and South Korean National Intelligence Service conspired “secretly and meticulously” in hatching their plot to use “radioactive or nano-poisonous substances” to assassinate Kim.

“We believe this extreme crime was orchestrated by hostile forces in order to damage North Korea’s domestic affairs,” Ambassador Ji Jae Ryong said.

Earlier this month, Pyongyang accused the two intelligence services of a failed plot to assassinate Kim with a biochemical bomb at a military parade in Pyongyang.

Last week, it demanded that the South hand over its spy chief.

South Korea has said it was unaware of what North Korea was referring to, while the CIA and the White House declined to comment on the May 6 statement from North Korea’s Ministry of State Security.

North Korea launched another ballistic missile on Sunday, which it said was aimed at verifying the capability to carry a “large-scale heavy nuclear warhead”, the latest in a series of tests that has increasingly alarmed its neighbors and raised tensions with the United States.

North Korea is believed to be developing an intercontinental ballistic missile capable of carrying a nuclear warhead and reaching the U.S. mainland, though the U.S. military’s Pacific Command said the type of missile fired on Sunday was “not consistent” with an ICBM.

“The test firing of ICBMs will occur at any time and place, at the will of North Korea’s highest leadership,” Ji said.