(Bloomberg) -- North Korea test-fired two suspected ballistic missiles about a week after it failed to put a spy satellite into orbit, in a show of defiance after the US sent a B-1B strategic bomber to airspace off the peninsula for military drills with South Korea.

Two short-range ballistic missiles were fired at about 11:40 p.m. and 11:50 p.m. Wednesday night from an area near Pyongyang’s main international airport toward waters off its east coast, South Korea’s Joint Chiefs of Staff said. The missiles flew about 360 kilometers (225 miles), and were “grave acts of provocation that undermine peace and stability,” it said in a statement to reporters.

North Korea said it retaliated for the dispatch of the bomber and the joint drills that it decried on state media Thursday morning as a preparation for a nuclear attack. 

Its missiles were being tested to deliver its own nuclear hit with air bursts at 400 meters (437 yards) above a target island. The drill was to simulate “scorched earth strikes at major command centers and operational airfields of the military gangsters” in South Korea, the state’s official Korean Central News Agency reported the General Staff of its Korean People’s Army as saying in a statement.

North Korea also issued a threat to the US and South Korea, saying Pyongyang was ready to punish them for “rash acts” and the US’s deployment of nuclear assets to the region.

After the missile launch, South Korea and US mobilized about 30 aircraft including F-35 stealth fighters for exercises that including air-to-ground live-fire training, South Korea’s Air Force said in a statement.

Pyongyang has bristled at US-South Korean joint military drills that started on Aug. 21 and run through the end of the month, calling them a prelude to invasion that could spur North Korea into action. 

The latest launches coincides with the drills and a meeting in mid-August among the leaders of the US, Japan and South Korea where they discussed ways to enhance their security cooperation and military training to respond to the nuclear and missile threats from Kim Jong Un’s regime in the North.

The US, Japan and South Korea on Tuesday held training at sea to practice hunting for missiles from the likes of North Korea in their first such exercise since the leaders of the three nations that Pyongyang lists as its mortal enemies pledged to improve their security cooperation.

North Korea last week failed for the second time in about three months to put a spy satellite into orbit when its rocket encountered troubles soon after launch, dealing a blow to Kim’s hopes of deploying a reconnaissance probe to keep an eye on US forces.

Read: North Korea Fails for Second Time to Launch Spy Satellite

Pyongyang had already fired 26 ballistic missiles and two space rockets so far this year. They included four intercontinental ballistic missiles that could hit the US mainland. Kim’s regime launched more than 70 ballistic missiles last year, a record for the state. 

Read: US Says Russia-North Korea Arms Deals Are ‘Actively Advancing’

Kim has ignored US calls to return to long-stalled nuclear disarmament talks. But he has been busy modernizing his arsenal of missiles and conducting tests of systems to attack South Korea and Japan, which host the bulk of US military personnel in the region.

North Korea launched two short-range ballistic missiles into waters off its east coast on July 19 after the USS Kentucky stopped in Busan, in the first visit to a port in South Korea in about four decades by a submarine capable of firing nuclear ballistic missiles. Pyongyang fired two more a few days later when another nuclear-powered US sub arrived at a separate South Korean port to replenish supplies. 

Those launches came after North Korea in July tested its Hwasong-18 solid-fuel ICBM. It flew longer than any of its other ICBMs and appeared designed to carry a multiple nuclear weapons payload, which increases the chances at least one bomb could slip past interceptors and make its way to a target.

A solid-fuel missile could be deployed quickly and fired with little warning. Liquid-fuel missiles in general take more time to prepare as propellant is added to their tanks, making them vulnerable to attack before taking off.

The US in June sent a nuclear-powered, guided-missile submarine to South Korea for the first time in six years for a show of force meant to deter North Korea from military strikes. The visit came after Yoon won assurances during a summit with Biden in April to strengthen extended deterrence measures, including more deployments of nuclear-armed submarines.

Displays of the US’s atomic assets are meant to serve as a reminder of a message Biden issued to leader Kim when the US president met with his South Korean counterpart and warned that a nuclear strike by North Korea would be suicidal.

Read: Kim’s Rare Display of Nuclear Warheads Sends Chilling Message

North Korea has demonstrated its missiles could fly as far as the US but there are questions as to whether the warheads would be able to stay intact to reach such distant targets.

--With assistance from Eunkyung Seo and Shinhye Kang.

(Updates with US-South Korea air drill.)

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