BUSAN, South Korea (AP) — The nuclear-powered aircraft carrier USS Ronald Reagan arrived in the South Korean port of Busan on Friday ahead of the two countries’ joint military exercise that aims to show their strength against growing North Korean threats.

The joint drills will be the first involving a United States (US) aircraft carrier in the region since 2017, when the USsent three aircraft carriers including the Reagan for naval drills with South Korea in response to North Korean nuclear and missile tests.

The allies this year have revived their large-scale military drills that were downsized or shelved in previous years to support diplomacy with Pyongyang or because of COVID-19, responding to North Korea’s resumption of major weapons testing and increasing threats of nuclear conflicts with Seoul and Washington.

The South Korean navy said the training is meant to boost the allies’ military readiness and show “the firm resolve by the Korea-US alliance for the sake of peace and stability on the Korean Peninsula.”

“The commitment of the US carrier strike group operating in and around the peninsula illustrates our commitment to stand together and our desire and focus ensuring that we are interoperable and integrated to face any challenge or threat whenever we are required,” Rear Adm. Michael Donnelly, commander of the carrier strike group, said in a news conference.

The North Korean threat is also expected to be a key agenda when U.S. Vice President Kamala Harris visits South Korea next week after attending the state funeral in Tokyo of slain former Japanese Prime Minister Shinzo Abe.

The Reagan’s arrival in South Korea comes after North Korean leader Kim Jong Un told Pyongyang’s rubber-stamp parliament this month he would never abandon his nuclear weapons and missiles he needs to counter what he perceives as U.S. hostility.

North Korea also passed a new law that enshrined its status as a nuclear power and authorised the preemptive use of nuclear weapons over a broad range of scenarios where the country or its leadership comes under threat.

Sung Kim, the Biden administration’s special representative for North Korea, met with South Korean counterpart Kim Gunn on Thursday in Seoul, where they expressed “serious concern” over the North’s escalating nuclear doctrine spelled out in the new law, South Korea’s Foreign Ministry said.

The diplomats reaffirmed the US commitment to defend South Korea in the event of a nuclear war with the full range of its military capabilities, including nuclear. The allies also maintained their months-old assessment that North Korea is gearing up to conduct its first nuclear test since 2017 and discussed “stern” countermeasures to such an action, the ministry said.

North Korea has dialled up weapons testing to a record pace in 2022, launching more than 30 ballistic weapons including its intercontinental ballistic missiles since 2017, as it exploits a divide in the UN Security Council deepened over Russia’s war on Ukraine.

While North Korea’s ICBMs garner much US attention because they pose a potential threat to the American homeland, the North has also been expanding its arsenal of nuclear-capable, shorter-range missiles designed to evade missile defences in South Korea.

North Korea’s expanding arsenal and threats of preemptive nuclear attacks have triggered concerns in South Korea over the credibility of the US “nuclear umbrella” protecting its allies in the event of war.

South Korean President Yoon Suk Yeol, a conservative who took office in May, has vowed to enhance South Korea’s conventional missile capabilities and work with the Biden administration to develop more effective strategies to deter North Korean attacks.

Senior US and South Korean officials met in Washington this month for discussions on the allies’ deterrence strategies and issued a statement reaffirming that “any (North Korean) nuclear attack would be met with an overwhelming and decisive response.” The statement said the United States reiterated “its ironclad and unwavering commitment to draw on the full range of its military capabilities, including nuclear (one)” to provide extended deterrence to South Korea.

North Korea has so far rejected US and South Korean calls to return to nuclear diplomacy, which have been stalled since 2019 over disagreements in exchanging the release of U.S.-led sanctions against the North and the North’s disarmament steps.

North Korea has harshly criticised Yoon for continuing military exercises with the U.S. and also for letting South Korean civilian activists fly anti-Pyongyang propaganda leaflets and other “dirty waste” across the border by balloon, even dubiously claiming the items caused its COVID-19 outbreak.

South Korean activists have continued to launch balloons after North Korea last month warned of “deadly” retaliation, triggering concern North Korea may react with a weapons test or even border skirmishes.

South Korea’s Unification Ministry, which deals with inter-Korean affairs, pleaded for activists to stop, citing safety reasons. Lee Hyo-jung, the ministry’s spokesperson, also said Friday that South Korea was prepared to sternly respond to any North Korean retaliation over leafleting.