The United States was expected to send B-1B Lancer strategic bomber jets to the Korean peninsula as part of air combat drills, a defence a source has told South Korea's Yonhap news agency.
The source would not say how many of the long-range supersonic bombers would participate in drills with South Korean fighter jets.
However, it is standard practice for the US to send two B-1Bs to the peninsula after North Korean provocations.
South Korea and the United States began five days of air combat drills on Monday, less than a week after Pyongyang tested an intercontinental ballistic missile it said put all of the US mainland within its reach.
The drills, which were planned before last week's missile test, involve more than 230 warplanes and 12,000 soldiers and are the largest such exercises yet carried out between the two allies.
North Korea has warned that the Vigilant Ace exercises are a provocation which would "only invite more terrible retaliation and precipitate their self-destruction."
The drills would include simulated precision strikes to take out mock North Korean nuclear and missile attacks, the South Korean Defence Ministry said according to Yonhap.
