In response, the North Korean military said it will use all possible measures to counter any attempts to decapitate its leader and collapse its regime, calling the planned joint drill "the height of hostile acts."

We "are ready to immediately and mercilessly punish without slightest leniency, tolerance and patience anyone provoking the dignified supreme headquarters even a bit," the Supreme Command of the Korean People's Army said in an English statement carried by the Korean Central Agency.

The first subject is South's presidential office, Cheong Wa Dae, the commander said, threatening to strike U.S. Asia-Pacific troops and the mainland as the next targets.

The defense ministry earlier said the planned drills will likely involve about 15,000 American soldiers, along with increased military assets, about twice the size of the exercise conducted last year.

The two allies have carried out annual joint exercises – Key Resolve and Foal Eagle -- since the 1990s to better deter North Korean aggression. The North claims the drills are a rehearsal for a northward invasion. (Yonhap)