The US military flew two strategic bombers over the Korean peninsula in a show of force late on Tuesday, as President Donald Trump met top defence officials to discuss how to respond to any threat from North Korea.
The two US Air Force B-1B bombers were joined by two F-15K fighters from the South Korean military after leaving their base in Guam, South Korea's Joint Chiefs of Staff said in a statement on Wednesday.
After entering South Korean airspace, the two bombers carried out air-to-ground missile drills in waters off the east coast of South Korea, then flew over the South to waters between it and China to repeat the drill, the release said.
The US military said in a separate statement it conducted drills with Japanese fighters after the exercise with South Korea, making it the first time US bombers have conducted training with fighters from both Japan and South Korea at night.
Tensions have soared between the United States and North Korea following a series of weapons tests by Pyongyang and a string of increasingly bellicose exchanges between Trump and North Korean leader Kim Jong-un.
The defence minister in Japan, a close military ally of the United States, said on Tuesday that Trump might take military action against North Korea as soon as next month.
"I think President Trump will judge in the middle of November how effective pressure and other efforts have been," Itsunori Onodera told reporters in Tokyo. "If there have been no changes from North Korea, it's possible that the US will take severe measures."
North Korea has launched two missiles over Japan and conducted its sixth nuclear test in recent weeks in pursuit of its goal of developing a nuclear-tipped missile capable of hitting the US mainland.
The US bombers had taken off from the Andersen Air Force Base in Guam. In August, Pyongyang threatened to fire intermediate-range missiles towards the vicinity of Guam, a US Pacific territory that is frequently subjected to sabre-rattling from the North.
South Korean and US government officials have been raising their guard against more North Korean provocations with the approach of the 72nd anniversary of the founding of North Korea's ruling party, which was on Tuesday.
Trump hosted a discussion on Tuesday on options to respond to any North Korean aggression or, if necessary, to prevent Pyongyang from threatening the United States and its allies with nuclear weapons, the White House said in a statement.
Trump was briefed by Secretary of Defense James Mattis and Chairman of the Joint Chiefs of Staff General Joseph Dunford at a national security team meeting, the statement said.