The B-1B combat bombers were joined by two South Korean F-15K fighter jets, and carried out air-to-ground missile drills off South Korean waters.
The move comes amid heightened tensions with North Korea over its nuclear program.
North Korea conducted its sixth nuclear test, and launched two missiles over Japan, in recent months.
The bombers took off from the US Pacific territory of Guam on October 10, before entering South Korean airspace and conducting firing exercises over the East Sea and Yellow Sea, South Korea’s military said.
The training was part of a program of “extended deterrence” against North Korea, it added.
The US said Japan’s air force also took part in the drill.
According to the White House, President Donald Trump met top officials from his national security team on Tuesday night for a briefing on ways to respond to threats from North Korea.
President Trump and North Korean leader Kim Jong-un have exchanged heated rhetoric in recent weeks.
In aspeech at the UN last month, President Trump accused Kim Jong-un of being “on a suicide mission” – while the North Korean leader responded by vowing to “tame the mentally deranged US dotard with fire”.
On October 11, a South Korean lawmaker said North Korean hackers had reportedly stolen a large cache of military documents from his country, including a plan to assassinate Kim Jong-un, and wartime contingency plans drawn up by the US and South Korea.
The South Korean defense ministry refused to comment about the allegation, while North Korea denied the claim.
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