SEOUL — North Korea is threatening its enemies with nuclear war in the wake of the arrival of an American aircraft carrier, the USS Carl Vinson, in the strategic port of Busan on Korea’s southeastern coast. As often in the past, the strident voice of the North Korean bluster is the younger sister of the country’s leader, Kim Jong-un.

“Constant deployment of U.S. strategic assets highlights urgency of the DPRK” — the Democratic People’s Republic of Korea — “to bolster up its self-defensive nuclear war deterrent,” is the headline on the website of Pyongyang’s Korean Central News Agency over the statement of Mr. Kim’s sister, Kim Yo-jong. Ms. Kim holds the modest title of vice department director of the Central Committee of the Workers’ party but is viewed as one of the North’s two or three most powerful leaders.

Enumerating a series of charges against America’s military role in the region, Ms. Kim said Washington’s “hostile policy” has not changed since President Trump’s inauguration. “As soon as its new administration appeared this year,” KCNA quoted her as saying, “the U.S. has stepped up the political and military provocations against the DPRK,” which she said is “carrying forward” the former administration’s “hostile policy.”

Offering her “justification for the DPRK to bolster up its nuclear war deterrent,” Ms. Kim neglected to mention Mr. Trump by name. Nor did she refer to South Korea’s impeached president, Yoon Suk-yeol, a strong advocate of war games, now in prison facing ouster by the constitutional court.

Mr. Yoon, along with his former defense minister and the former commander of the Defense Intelligence Command, also face the criminal charge of “insurrection” for Mr. Yoon’s abortive attempt at imposing martial law in December. In addition, prosecutors are considering treason charges against all three.

The chaos is not stopping the Carl Vinson, accompanied by a guided missile cruiser and an Aegis-equipped destroyer, from participating in war games with American and South Korean forces — the first major exercises in and around Korea since Mr. Trump’s inauguration in January.

Mr. Yoon’s government, still putting on an appearance of functioning normally, was eager to welcome the Carl Vinson as the prelude to a large-scale annual show of force called “Freedom Shield,” planned well before Mr. Yoon’s impeachment stripped him of the power but not the title of president.

Unbowed in the midst of uncertainty about the future of the current government, the South’s defense ministry accused the North of “sophistry to justify its nuclear development and future provocations.” The statement, which would normally have gone out under the name of the defense minister, was unsigned.

The ministry placed its confidence in the Korean-American alliance without alluding to Mr. Trump, who has said he would like to see Kim Jong-un again in the quest for reconciliation with the North. “Should the North conduct provocation, using Seoul and Washington’s just and defensive military activities as pretext, it will be met with overwhelming retaliation,” the statement as quoted by Yonhap News said.

The South’s show of defiance reflects the strong bonds that Mr. Yoon, at the height of his presidency, formed with President Biden at Washington and at a trilateral summit at Camp David that also included Japan. The result was much strengthened war games that Mr. Trump had canceled after the first of his three summits with Kim Jong-un in Singapore in June 2018.

Mr. Yoon’s predecessor, the leftist Moon Jae-in, was fine with the policy against joint exercises as he pursued North-South reconciliation in vain after the impeachment and ouster of the conservative Park Geun-hye in 2017. The conservative Mr. Yoon reversed that policy after his election by a narrow margin in March 2022.

The commander of the carrier strike group, Rear Admiral Michael Wosjek, avoided any comment on the future of cooperation with Korea or Japan when meeting the press aboard the Carl Vinson. Rather, Yonhap reported, he said he was confident the strike group “would continue efforts for the shared objective of peace, prosperity and stability, and reaffirming the U.S. commitment to the alliance.”