The US has flown a B-52 bomber over its ally South Korea, just days after claims from North Korea that it had tested a hydrogen bomb.
The low-level flight will be seen as a clear show of force, as the bomber is capable of delivering nuclear weapons.
A fly-over also happened after North Korea's third nuclear test in 2013.
North Korean authorities claimed to have successfully detonated a hydrogen bomb on Wednesday. However, weapons experts and The White House have expressed doubts over to what type of bomb it actually was.
North Korean media, cited by BBC, quoted the country's leader Kim Jong-Un saying the test was the "legitimate right of a sovereign state and a fair action that nobody can criticise".
Announcing the B-52 flight, Lt Gen Terrence O’Shaughnessy of United States Forces Korea said, "the US maintains an ironclad commitment to the defence of our partner nation, and this combined mission demonstrates the strength of the alliance between the United States and the Republic of Korea and the resolve of both nations to maintain stability and security on the Korean Peninsula".
The United Nations (UN) Security Council has begun working on a resolution proposing further measures and sanctions against North Korea in the wake of the alleged hydrogen bomb test.
