SEOUL, South Korea — The powerful younger sister of North Korean leader Kim Jong Un attended a public event in Pyongyang for the first time in more than 50 days, casting further doubt on media speculation that he had ordered her to lay low over the failed nuclear summit with Washington.

North Korea's state media on Tuesday showed Kim Yo Jong clapping aside her brother, his wife and other top officials at the 150,000-seat May Day Stadium, where thousands of gymnasts, dancers and flip-card-wielding spectators worked in precise unison to perform "The Land of the People."

The official Korean Central News Agency said the performers on Monday showed "beautiful and graceful rhythmic movements, high-spirited gymnastics, interesting national emotion and rich artistic depiction," but also that Kim Jong Un was quite unhappy about their display. He seriously criticized the creators for their "wrong spirit of creation and irresponsible work attitude" and set forth "important tasks" to correctly implement the country's revolutionary policy on literature and art, KCNA said.

State media often reports on Kim scolding factory officials, educators and others perceived as not performing to his standards. The mass games events were once routine in North Korea but were on hiatus for several years during the mourning for Kim's father and only returned last year.

Kim Yo Jong is a senior official of North Korea's ruling party and is believed to be her brother's closest confidant. She had accompanied him to his summits with President Donald Trump and South Korean President Moon Jae-in and had joined other dignitaries in the stands at last year's Winter Olympics in South Korea.

But speculation about her status grew after she was left out from her brother's trip to Vladivostok, Russia, in April for a summit with Russian President Vladimir Putin. North Korean media had last shown her at a meeting of the North's rubber-stamp parliament on April 12.

South Korea's conservative Chosun Ilbo newspaper last week cited an unidentified source in reporting that Kim Jong Un had ordered his sister to lay low following the collapse of his summit with Trump in February over what the Americans described as excessive North Korean demands for sanctions relief in exchange for only a partial surrender of its nuclear capabilities.

North Korean official Kim Yong Chol, second from right, and a clapping Kim Jong Un, center, sitting in the same row along with other top officials during a musical performance by the wives of Korean People's Army officers Sunday, June 2, 2019. The senior North Korean official who had been reported as purged over the failed nuclear summit with Washington was shown in state media on Monday enjoying a concert near leader Kim. (KRT via AP Video)
North Korean official Kim Yong Chol, second from right, and a clapping Kim Jong Un, center, sitting in the same row along with other top officials during a musical performance by the wives of Korean People's Army officers Sunday, June 2, 2019. The senior North Korean official who had been reported as purged over the failed nuclear summit with Washington was shown in state media on Monday enjoying a concert near leader Kim. (KRT via AP Video)

The newspaper also reported that Kim had punished his former top nuclear envoy, Kim Yong Chol, who North Korean media showed at the mass games and at a weekend concert of military wives. Senior envoy Kim Hyok Chol, who the Chosun reported had been executed along with four Foreign Ministry officials for betrayal, has not been seen by the media since the end of the Trump-Kim summit in Hanoi, Vietnam, in February.

Nuclear negotiations have been at a standstill since the summit's collapse and Kim in recent weeks has dialed up pressure on Washington by resuming weapons tests and setting an end-of-year deadline for the Trump administration to offer mutually acceptable terms for a deal to salvage the diplomacy.

Kim and Trump initially met in Singapore last June, signing a vague statement on improved bilateral relations and a nuclear-free Korean Peninsula without describing how or when it would occur.

In a statement issued Tuesday by an unidentified foreign ministry spokesman, North Korea accused the United States of betraying the Singapore agreement and causing the breakdown in Hanoi by demanding that the North unilaterally surrender its nuclear weapons. The spokesman called for the United States to change its "current method of calculation" and warned there was a limit to the North's patience.

"At the second DPRK-U.S. summit talks held in Hanoi amid the great interest and expectation of the entire world, the United States made the biggest mistake of having missed a lifetime opportunity by insisting on 'dismantlement of the nuke first,'" the statement said, referring to North Korea by its formal name, the Democratic People's Republic of Korea. "This overshadows the future of the DPRK-U.S. talks."

South Korea's government and media have a mixed record on tracking developments among North Korea's ruling elite, made difficult by Pyongyang's stringent control of information about them. Although North Korea has previously banished or executed scapegoats to atone for major political flops, experts doubted the recent reports, saying such extreme punishments were unlikely unless Kim Jong Un was abandoning negotiations with the United States.

Cheong Seong-Chang, an analyst at South Korea’s Sejong Institute, said Kim Yo Jong would not have been seen at the Supreme People’s Assembly meeting in April had she been disciplined over the summit failure. Cheong said it’s more likely she was reappearing after a period of rest.