The US has flown two bomber jets over the Korean peninsula despite threats from the Kim Jong-un regime that they will be shot down.
Six military planes, including two American supersonic B-1B bombers, took part in a drill on Tuesday night, according to Yonhap news agency.
The bombers from Guam staged a simulated air-to-ground missile firing drill with two F-15K fighters, according to senior US defence officials.
It is the latest provocation amid heightened tensions between the US and North Korea.
Last month, foreign minister Ri Yong Ho accused the United States of having declared war.
In a rare press appearance at the United Nations in New York, he said: “The whole world should clearly remember it was the US who first declared war on our country.
“Since the United States declared war on our country, we will have every right to make countermeasures, including the right to shoot down United States strategic bombers even when they are not inside the airspace border of our country.”
Earlier it emerged North Korean hackers are feared to have stolen a huge haul of classified military documents – including detailed plans revealing what the US and South Korea would do if the countries went to war.