North Korea views the drills as a rehearsal for invasion, which have in the past included gaming a nuclear attack by the US, and the direct targeting of leader Kim Jong Un.
US President Joe Biden is still in his honeymoon period just a few weeks in office, and North Korea has remained patient as it seeks talks on relief from US-led sanctions over its nuclear weapons program. The concern is that joint US-South Korea military drills may damage prospects for future negotiations.
North Korea has previously conducted nuclear or long range missile tests within weeks of a new US president taking office. In a 2018 deal with the Trump administration, North Korea suspended its long-range missile and nuclear weapons testing, but activists say Pyongyang has so far received little in return.