A North Korea-focused news site reported Tuesday on the “unusual” activity throughout April of leisure boats often used by leader Kim Jong Un in the coastal resort of Wonsan, suggesting his presence there amid ongoing speculation about his health.

NK News said satellite imagery showed this week that the boats “have been active throughout this month and made unusual moves” around the time of April 14, when Pyongyang is believed to have carried out a missile test.

When the boats relocate from central Wonsan to where his villa is situated, “there has been a high correlation with Kim’s public appearances in the area,” the news site said.

Kim’s movements have not been reported in state-run media since April 12, when the Korean Central News Agency said he had presided over a meeting of the Political Bureau of the Central Committee of the ruling Workers’ Party of Korea, held the day before.

On April 14, South Korea said the North on the same day fired several projectiles that appeared to be short-range cruise missiles into the Sea of Japan from an area near the coastal town of Munchon in Kangwon Province, whose capital city is Wonsan.

North Korea’s official media, however, have not reported on the missile launch, raising doubts about Kim’s health, but fear of the coronavirus could have been keeping Kim out of public sight, a South Korean minister and U.S. sources said Tuesday.

South Korean Unification Minister Kim Yeon-chul, who oversees engagement with North Korea, said it was plausible Kim that decided against attending due to the coronavirus, given stringent steps his government has taken to head off an outbreak.

“He had never missed the anniversary for Kim Il Sung’s birthday since he took power, but many anniversary events including celebrations and a banquet had been canceled because of coronavirus concerns,” the minister told a parliamentary hearing.

“I don’t think that’s particularly unusual given the current (coronavirus) situation,” the minister said, although North Korea has said it has no confirmed cases of the coronavirus.

An authoritative source familiar with U.S. intelligence assessments said credible reports to the U.S government suggested the reason Kim’s presidential train had been spotted near a presidential retreat in Wonsan last week was that Kim had been staying there to avoid catching the virus.

U.S. government experts lacked categorical evidence to prove this, but were for the most part dismissing media reports suggesting that Kim had contracted some kind of serious illness, the source said.

Kim Yeon-chul described reports that Kim had undergone a heart procedure, and that a Chinese medical team had travelled to North Korea, as “fake news.”

A U.S. official, who spoke on condition of anonymity, said Washington’s view was largely in line with the South Korean minister’s assessment.

Prime Minister Shinzo Abe said Tuesday he is following the news with “great interest.

Japan and the United States have been in “very close” communication, Abe told a parliamentary session. He declined to say whether he knows how Kim is doing.

“I’m paying attention (to the issue) with great interest,” Abe said during a session of the Lower House budget committee.

North Korea abducted Japanese nationals in the 1970s and 1980s and resolving the decadeslong issue has been one of Abe’s top diplomatic priorities. The Japanese leader wants to meet with Kim face-to-face to break the impasse but no summit has been held so far.

Last week, CNN reported that the United States was monitoring intelligence that Kim was in grave danger after surgery, but Seoul claims that no unusual signs have been detected in Pyongyang and U.S. President Donald Trump has said he thinks “the report was incorrect.”

On Sunday, meanwhile, Moon Chung-in, the top foreign policy adviser to South Korean President Moon Jae-in, told U.S. media that Kim is well and has been staying in Wonsan since April 13.

In 2014, Kim was absent from public view for around 40 days, leading foreign affairs experts to speculate that he was suffering health problems.

Under Kim’s rule since 2011, North Korea has expanded its arsenal of nuclear weapons and long-range missiles, and with no obvious successor, any change in leadership in the secretive, authoritarian state would raise concerns about instability that could impact other North Asian countries and the United States.

North Korea has responded to the global coronavirus pandemic by cancelling some large events and imposing a border lockdown and quarantine measures.

If Kim Jong Un is hiding out due to fears surrounding COVID-19, it would “puncture a hole in the state media narrative of how this crisis has been perfectly managed”, said Chad O’Carroll, CEO of Korea Risk Group, which monitors North Korea.

“If he is merely trying to avoid infection, it should theoretically be very easy to release photos or videos of a healthy looking Kim,” he said.