The South Korean army's K-55 self-propelled artillery vehicles take part in a military exercise near the demilitarised zone separating the two Koreas in Paju, South Korea, November 29, 2017 (Photo: REUTERS/Kim Hong-Ji)

The annual U.S.-South Korean drill, called Vigilant Ace, will run until Friday, with more than 230 aircraft taking part. The exercises have been condemned as a provocation by North Korea. Around 12,000 U.S. service members, including those from the Marines and Navy, will join South Korean troops. South Korean media reports said B-1B Lancer bombers could join the exercise this week. North Korea's Committee for the Peaceful Reunification of the Country said the drill would "push the already acute situation on the Korean peninsula to the brink of nuclear war".