 South Korea and the US conducted a joint air drill on April 21 as a part of their ongoing large-scale combined air drills to deter North Korea's provocations, according to the South Korean military. A video provided by the South Korean Defense Ministry showed various South Korean and US jet fighters flying in formation in the air and pilots from the two countries attending a briefing before the drills. The exercise kicked off on April 17 for a 12-day run. Tension has flared as North Korea has ramped up military activities and threatened more practical and offensive action as US and South Korean forces hold annual spring military exercises it called a rehearsal for an all-out nuclear war.