North Korea's decision to sit out the Tokyo Olympics this summer due to COVID-19 fears will likely prolong the diplomatic deadlock with neighboring Japan and South Korea and could delay the resumption of denuclearization talks with the United States.

The announcement on a website run by North Korea's sports ministry on Tuesday is a lost opportunity for a breakthrough in Tokyo's efforts to secure the return of citizens abducted by Pyongyang in the 1970s and 1980s.

Japanese Prime Minister Yoshihide Suga speaks to reporters at his office in Tokyo on March 25, 2021, after the government confirmed North Korea fired two ballistic missiles. (Kyodo) ==Kyodo

North Korea's participation in the 2018 Pyeongchang Winter Games in South Korea, with leader Kim Jong Un's sister visiting as a special envoy, was the catalyst for a diplomatic rapprochement that culminated in a series of historic summits with then U.S. President Donald Trump.

South Korean President Moon Jae In had been eager for a similar breakthrough at the Tokyo Olympics, viewing it as another chance to serve as a bridge between Pyongyang and Washington.

The Unification Ministry on Tuesday expressed regret at the decision, while saying it would continue efforts for dialogue. A spokesman at South Korea's Foreign Ministry said there is "still time" for North Korea to change its mind.

The announcement came as the administration of Trump's successor, Joe Biden, reviews its approach to North Korea after negotiations failed in 2019 due to disagreement over the level of sanctions relief the country would receive in exchange for scaling down its nuclear and missile programs.

U.S. President Joe Biden talks to reporters as he departs the White House on March 26, 2021 in Washington. (Getty/Kyodo)

Kim had previously expressed willingness to send athletes to the Tokyo Olympics, giving Japan a rare chance to engage with North Korea.

Suga has called the abduction issue a top priority for his administration, vowing not to "waste any chance" for dialogue with Pyongyang and expressing willingness to meet with Kim "without preconditions."

Japan officially lists 17 nationals as having been abducted by North Korean agents, including five who have been repatriated, but suspects their involvement in many more disappearances.

The efforts have been deadlocked after a 2014 agreement to investigate the fate of victims fell apart. Meanwhile, Tokyo has felt a growing sense of urgency to resolve the issue as members of their immediate families grow older.

An official at the prime minister's office said the announcement, which came on the same day Japan extended its unilateral sanctions on North Korea by two years, could be a sign Pyongyang was annoyed by the lack of overtures from Tokyo.

"They may have thought they would lose face by participating in the Tokyo Olympics despite the sanctions. This is a lost opportunity on Japan's part," the official said.

Meanwhile, a senior Defense Ministry official voiced concern the nonparticipation of North Korean athletes would allow Pyongyang to make provocations such as ballistic missile tests during the Summer Games.

"We will be on the alert in coordination with the United States and South Korea," the official said.

Other Japanese government officials said North Korea's announcement was not surprising because the country has closed its borders since early last year to prevent COVID-19 from being brought in from abroad.

North Korean leader Kim Jong Un attends a plenary meeting of the Central Committee of the ruling Workers' Party on Feb. 8, 2021. (KCNA/Kyodo)

While vaccination efforts are being stepped up around the world, North Korea is believed to be particularly vulnerable to outbreaks because of its weak medical system, and diplomacy will not be a priority in the near term, said Satoru Miyamoto, an expert on North Korea at Seigakuin University.

North Korea claims no coronavirus cases have been confirmed in the country, while Japan has seen daily infections rise back above 2,000 since lifting a state of emergency covering Tokyo and other regions last month.

"Calling for dialogue won't work unless North Korea decides the COVID-19 scare is over. We don't know when that will be, and until then the situation will remain at a standstill," Miyamoto said.