The exercise, which involved a US nuclear-weapons-capable B-52 bomber, comes as Seoul, Washington and Tokyo beef up their defence cooperation against growing missile and nuclear threats from North Korea.

The US bomber landed at a South Korean airbase on Tuesday after a flyover at the country's largest defence exhibition.

B-52s, which fly at subsonic speeds, can travel more than 8,800 miles without refuelling, at an altitude reaching 50,000 feet.

The trilateral exercise took place south of the Korean peninsula, where Seoul and Tokyo's air defence identification zones overlap, according to the South Korean Air Force.

"This marks the first time for the air powers of South Korea, the United States, and Japan to carry out an aerial exercise," it said in a statement.

The exercise was "planned to expand the three countries response capabilities against North Korea's growing nuclear and missile threats," the statement added.

Pyongyang views all such exercises as rehearsals for an invasion and has repeatedly warned it would take "overwhelming" action in response.

North Korea baulks at Washington's deployment of long-range military assets and in 2017 threatened to "shoot down" US strategic bombers even outside North Korean airspace.

The B-52's arrival followed a port visit a week earlier by the nuclear-powered aircraft carrier USS Ronald Reagan, which provoked an angry response from Pyongyang.

It also landed ahead of Russian Foreign Minister Sergei Lavrov's two-day visit to Pyongyang, as the UN-sanctioned neighbourbors and historic allies tighten ties.

Moscow is believed to be interested in buying North Korean ammunition, while Pyongyang wants Russia's help to develop its internationally condemned missile programme.

In the face of a record-breaking series of weapons tests by Pyongyang this year, Seoul has moved to strengthen its security relationship with traditional ally the United States while entering a trilateral defence arrangement that also includes Japan.

In August, the leaders of the three countries met for a summit at Camp David, agreeing to a multi-year plan of regular joint exercises and to share real-time data on North Korea.

Earlier this month, the three countries staged a joint maritime drill around the Korean peninsula for the first time in seven years.

That two-day drill simulated intercepting North Korean smuggling vessels, according to Seoul's navy.