SEOUL, South Korea — The United States deployed a B-52 bomber on a low-level flight over its ally South Korea Sunday, a show of force following North Korea’s nuclear test last week.

North Korean leader Kim Jong Un maintained that Wednesday’s test was of a hydrogen bomb and said it was a self-defensive step against a U.S. threat of nuclear war.

North Korea’s fourth nuclear test angered both China, its main ally, and the U.S., although the U.S. government and weapons experts doubt the North’s claim that the device was a hydrogen bomb.

The massive B-52, based in Guam and capable of carrying nuclear weapons, could be seen in a low flight over Osan Air Base at around noon local time. It was flanked by two fighter planes, a U.S. F-16 and a South Korean F-15, before returning to Guam, the U.S. military said in a statement.

Osan is south of Seoul and 48 miles from the Demilitarized Zone that separates the two Koreas. The flight was “in response to recent provocative action by North Korea,” the U.S. military said.

“The United States remains steadfast in its commitment to the defense of the Republic of Korea [South Korea] and to maintaining stability on the Korean Peninsula, to include extended deterrence provided by our conventional forces and our nuclear umbrella,” U.S. Lt. Gen. Terrence O’Shaughnessy said.

After North Korea’s last test, in 2013, the U.S. sent a pair of nuclear-capable B-2 stealth bombers over South Korea. At the time, the North responded by threatening a nuclear attack on the U.S.

The U.S. also is considering sending a nuclear-powered aircraft carrier to waters off the Korean peninsula next month to join a naval exercise with Seoul, South Korea’s Yonhap news agency reported without identifying a source. U.S. Forces and South Korea officials, however, said they had no knowledge of the plan.

The two Koreas remain in a technical state of war after their 1950-53 conflict ended in a truce, not a peace treaty, and the U.S. has about 28,500 troops based in South Korea.

An editorial in the North’s Rodong Sinmun newspaper on Sunday called for a peace treaty with the U.S., which is the North’s long-standing position. “Only when a peace treaty is concluded between the DPRK [North Korea] and the U.S. can genuine peace settle in the Korean Peninsula,” state news agency KCNA quoted it as saying.

The North’s official name is the Democratic People’s Republic of Korea.

The U.S. and China have both dangled the prospect of better relations, including the lifting of sanctions, if North Korea gives up its nuclear weapons.

Earlier on Sunday, KCNA quoted Kim as saying no one had the right to criticize the North’s nuclear tests.

“The DPRK’s H-bomb test … is a self-defensive step for reliably defending the peace on the Korean Peninsula and the regional security from the danger of nuclear war caused by the U.S.-led imperialists,” it quoted Kim as saying.

“It is the legitimate right of a sovereign state and a fair action that nobody can criticize,” he said.

Timing of test

Kim’s comments were in line with North Korea’s official rhetoric blaming the U.S. for deploying nuclear weapons on the Korean peninsula to justify its nuclear program but were the first by its leader since Wednesday’s blast.

The U.S. has said it has no nuclear weapons stationed in South Korea.

Kim noted the test was being held ahead of a rare congress of its ruling Workers’ Party later this year, “which will be a historic turning point in accomplishing the revolutionary cause of Juche,” according to KCNA.

Juche is the North’s home-grown state ideology that combines Marxism and extreme nationalism established by the state founder and the current leader’s grandfather, Kim Il Sung.

KCNA said Kim made the comments on a visit to the country’s Ministry of the People’s Armed Forces.

South Korea continued to conduct high-decibel propaganda broadcasts across the border into the North Sunday.

The broadcasts, which include “K-pop” music and statements critical of the Kim regime, began Friday and are considered an insult by Pyongyang. A top North Korean official told a rally Friday that the broadcasts had pushed the rival Koreas to the “brink of war.”

Daily life was mostly as normal on the South Korean side of the border Sunday. A popular ice fishing festival near the border attracted an estimated 121,300 people Saturday and another 100,000 Sunday, Yonhap reported.