Kim Jong un
Kim Jong unReuters

North Korea on Tuesday reportedly threatened the United States and South Korea of "pre-emptive strike" if their military exercise proves to be a threat to Pyongyang, Yonhap reported. In response, South Korea said the country "would firmly respond to North Korea's reckless provocations."

After North Korea's nuclear test and rocket launch, the US and South Korea decided to conduct a joint military exercise in March. North Korea called the proposed military drill a call for war and said it would first target South Korea's presidential Blue House and the troops in Asia-Pacific and on the U.S. mainland.

We "are ready to immediately and mercilessly punish without slightest leniency, tolerance and patience anyone provoking the dignified supreme headquarters even a bit," Yonhap quoted the Supreme Command of the Korean People's Army as saying.

"All the powerful strategic and tactical strike means of our revolutionary armed forces will go into pre-emptive and just operation to beat back the enemy forces to the last man if there is a slight sign of their special operation forces and equipment moving to carry out the so-called 'beheading operation' and 'high-density strike,'" the Supreme Command said, according to Reuters.

The annual joint military drill of the U.S. and South Korea, Key Resolve and Foal Eagle, will start on March 7 and last till  April 30. At least 15,000 U.S. troops and 290,000 South Korean personnel will take part in the drill.

The measures were taken after North Korea defied the United Nations resolutions and launched a long-range missile on Feb. 7 and tested a miniaturised hydrogen bomb earlier on Jan. 6.