SEOUL: A nuclear-powered US aircraft carrier arrived in South Korea on Wednesday (March 15) for joint military exercises, the US Navy said, in the latest show of force against the North.

The USS Carl Vinson berthed in the southern port of Busan as US Secretary of State Rex Tillerson began a tour of the region, where tensions have spiked in recent weeks with missile launches from the nuclear-armed North and the brazen assassination of Kim Jong Un's half-brother in Malaysia.

Pyongyang has long condemned the annual joint drills, which involve tens of thousands of troops, as provocative rehearsals for invasion, while Seoul and Washington insist they are purely defensive in nature.

The aircraft carrier and a US destroyer will conduct naval drills including an anti-submarine manoeuvre with South Koreans in waters off the Korean peninsula as part of the annual Foal Eagle exercise.

Yonhap news agency said the navy drills will kick off next week.

"The importance of the exercise is to continue to build our alliance and our relationship and strengthen that working relationship and interoperability between our ships," Rear Admiral James Kilby, commander of USS Carl Vinson Carrier Strike Group 1, told journalists.

He said training opportunities in the region were "world-class" and allow the US to "build upon our strong alliance" with the South.

The North's official KCNA news agency said Tuesday that "all US military strategic assets including its aircrafts are within the cross hair of our powerful, precision striking means".

In an apparent response to the exercises, Pyongyang launched four ballistic missiles last week - with three landing in waters that are part of Tokyo's exclusive economic zone - and described them as a drill for an attack on US bases in Japan.

Visiting the headquarters of an army unit early this month, the North's leader Kim Jong-Un praised his troops for their "vigilance against the US and South Korean enemy forces that are making frantic efforts for invasion", according to the North's official KCNA news agency.

Kim also ordered the troops to "set up thorough countermeasures of a merciless strike against the enemy's sudden air assault", it said.

Pyongyang is widely seen as behind the murder of Kim's half-brother Kim Jong-Nam in Kuala Lumpur last month, by two women using a banned nerve agent.

Washington and Seoul have agreed to deploy the Terminal High Altitude Area Defense (THAAD) missile defence system to counter growing nuclear and missile threats by the North, and the first parts have recently arrived in the South.

The plan has angered Beijing, which fears it will undermine its own ballistic capabilities, with China's foreign ministry saying THAAD "jeopardises the strategic security interests" in the region and warning of "consequences" for Seoul and Washington.

Last year, the impoverished but nuclear-armed North staged two atomic tests and a number of missile launches.

The most recent missile test on Feb 12 - the first since US President Donald Trump took office - showed some signs of progress in its missile capabilities, according to the South Korean military.

Participation in the joint exercises is similar to last year when they involved 300,000 South Korean and around 17,000 US troops, as well as strategic US naval vessels and air force assets, a US military spokesman said.

A computer-based simulation portion of the joint exercises started Monday, while the field-centred Foal Eagle runs until the end of April. - AFP