Pyongyang declared a "preemptive nuclear strike of justice" against allies South Korea and the US in a statement released Monday through its state news agency, citing leader Kim Jong Un.

"The indiscriminate nuclear strike... will clearly show those keen on aggression and war, the military mettle of (North Korea)," the statement said.

"If we push the buttons to annihilate the enemies even right now, all bases of provocations will be reduced to seas in flames and ashes in a moment," the North's statement said further.

'Largest ever' military drills

The threat was made just hours before the two allies kicked off joint military drills on Monday, with South Korea's Yonhap news agency reporting that they would be the "largest ever."

More than 300,000 South Korean and 17,000 US troops are said to be taking part. The military exercises "Foal Eagle" and "Key Resolve," which prepare allied troops against a potential strike from the North, should last until the end of April.

North Korea has condemned the annual military drills as "offensive rehearsals for an invasion." South Korea and the US have maintained that the exercises are purely defensive.

North Korea said further that the war drills are aimed at infringing "upon the sovereignty" of the country.

The drills were expanded after North Korea's fourth nuclear test on January 6 and February's rocket launch, which was seen by the international community as a disguised ballistic missile test.

The UN Security Council imposed tough sanctions in response to Pyongyang's recent nuclear and ballistic missile tests. The measures include the ban on sales of weapons to the North, travel bans and asset freezes on selected individuals, and the inspection of North Korean cargo.

Pyongyang has rejected the sanctions, and in response fired six short range missiles into the sea last week. North Korean leader Kim Jong Un had ordered his country's nuclear arsenal to be on standby.

smm/lw (dpa, AFP)