To show protestation US flew two bombers over South Korea in a show of force against North Korea over its nuclear testing.
The supersonic B-1B Lancers were escorted by US and South Korean fighter jets when they entered airspace south of Seoul on Tuesday.
The aircraft flew to South Korea from Anderson Air Force Base in the US territory of Guam.
After the show of force, General Vincent Brooks, US-South Korea Combined Forces Command, said the US has an “unshakable commitment to defend allies in the region”.
He said: “Today’s demonstration provides just one example of the full range of military capabilities in the deep resources of this strong alliance to provide and strengthen extended deterrence.”
Brooks added: “North Korea’s nuclear test is a dangerous escalation and poses an unacceptable threat.”
He said the US “will take necessary steps” to defend its allies with measures including operations like Tuesday’s flyover and the deployment of the Terminal High Altitude Air Defense (THAAD) battery to the Korean Peninsula.