U.S. and North Korean national flags are seen at the Capella Hotel on Sentosa island in Singapore June 12, 2018.
U.S. and North Korean national flags are seen at the Capella Hotel on Sentosa island in Singapore June 12, 2018. Reuters / Jonathan Ernst

The USS Abraham Lincoln aicraft carrier led military exercises in the Yellow Sea, and air defence artillery at Osan air base intensified drills, U.S. forces in Asia said on Tuesday amid signs of an imminent North Korean long-range missile test.

Tension on the Korean Peninsula has been growing amid speculation North Korea could test its largest intercontinental ballistic missile (ICBM) at full range as soon as this week, after threatening to break a self-imposed 2017 moratorium on long-range missile and nuclear testing.

In a demonstration of air power in international airspace on Tuesday, the U.S. Indo-Pacific Command (INDOPACOM) mobilised fighter jets from the USS Abraham Lincoln Strike Group along with other regionally based Air Force planes.

U.S. Forces Korea (USFK) also said that in response to North Korea's recent missile tests its air defence artillery brigade at Osan air base had increased the intensity of its certification exercise to demonstrate its capabilities.

"DPRK's significant increase in its missile testing activity undermines peace, security and destabilises the Northeast Asia region," USFK said, using the acronym of North Korea's official name, the Democratic People's Republic of Korea.

"While this type of training is routinely conducted by U.S. Patriot batteries ... its increased intensity of its certification underscores the seriousness USFK takes against the DPRK's recent missile launch behaviour," USFK said.

On Friday, Washington and Seoul said in a rare joint announcement that North Korea had used its largest-ever ICBM in two recent launches. Pyongyang said the launches were conducted as preparations for a satellite launch.

Those launches did not demonstrate the missile's full range, and analysts said the North might have used only one stage of the missile or adjusted its fuel volume to fly at lower altitudes.

The missile system, the Hwasong-17, was unveiled at a military parade in 2020 and reappeared at a defence exhibition in October 2021.

"The ICBM launches by DPRK are a brazen violation of multiple U.N. Security Council resolutions - as well as its international commitments - and pose a threat to regional neighbours and the international community," INDOPACOM said in a statement.

A spokesman for South Korea's defence ministry said it was also closely monitoring North Korea's movements and maintaining a robust combined readiness posture with the U.S. military.