North Korea on Sunday threatened “indiscriminate” nuclear strikes against South Korea and the United States if the two allies push ahead with joint military drills scheduled to begin Monday, AFP reports.

The threat to carry out what it described as a “pre-emptive nuclear strike of justice” was made in a statement by North Korea’s powerful National Defense Commission, citing the Supreme Command of the Korean People’s Army (KPA).

It comes just days after leader Kim Jong-Un ordered the country’s nuclear arsenal to be placed on standby for use “at any moment,” in response to tough new UN sanctions imposed over the North’s fourth nuclear test in January and last month’s long-range rocket launch.

The United States downplayed Kim’s order and said it had “not seen North Korea test or demonstrate the ability to miniaturize a nuclear weapon and put it on an ICBM (intercontinental ballistic missile).”

Pyongyang has issued dire warnings of nuclear attack in the past, usually during periods of elevated military tensions of the Korean peninsula, noted AFP.

While the North is known to have a small stockpile of nuclear warheads, experts are divided about its ability to mount them on a working missile delivery system.

The national Defense Commission described the annual South Korea-U.S. military exercises as “undisguised nuclear war drills” that threatened the North’s national sovereignty, and vowed an all-out offensive in response.

“The indiscriminate nuclear strike… will clearly show those keen on aggression and war, the military mettle of (North Korea),” said the statement published by the North’s official KCNA news agency.

On January 6, North Korea carried out a nuclear test and claimed to have been testing a hydrogen bomb. Weeks later it launched a long-range rocket, in violation of earlier UN sanctions.

The United States originally expressed skepticism over Pyongyang’s claims that it tested a hydrogen bomb during the January 6 test, but later changed its mind after further review and analysis of the intelligence information.