America has scrambled five spy planes to monitor North Korea amid rumours that Kim Jong Un is gravely ill or has died.
Four eavesdropping aircraft will try to intercept messages about the Supreme Leader and his health, while one ground surveillance plane will monitor for unusual troop movements.
South Korea has also deployed a spy aircraft over its northern neighbour, the Chosun Ilbo newspaper reported, despite Seoul's insistence that Kim is alive and well.
Kim Yeon-chul, South Korea's minister for North Korean affairs, continued to downplay rumours about Kim on Tuesday - saying he had likely disappeared to avoid catching coronavirus and not because he is currently ill.
Speculation has been swirling around the North Korean dictator since April 15, when he missed a Day of the Sun celebration honouring his grandfather Kim Il-sung.
Kim was last seen in public on April 11, presiding over a meeting of North Korea's ruling Workers' Party.
There have been reports that Kim had heart surgery and was subsequently critically ill or even dead, but none of these have been confirmed.
Off the back of those rumours, America has reportedly sent three Beechcraft RC-12 Guardrail planes and one EO-5C 'Crazy Hawk' to scout over North Korea.
Both types of aircraft are designed to intercept electronic communications.
The US has also sent a Northrop Grumman E-8 Joint STARS aircraft, which is used to collect imagery and track ground movements.
South Korea has also sent one aircraft though it is not clear what kind, a senior military source told Chosun Ilbo.
Kim's name has continued appearing in the country's state-run media but an absence of photos of the leader has led to suspicions mounting.
North Korea's daily newspaper Rodong Sinmun routinely publishes photos of Kim going about his daily activities.
Kim's last lengthy disappearance from public view came in October 2014, when he vanished for six weeks - believed to be while he had surgery on his ankle.
His current whereabouts are unknown, but satellite imagery showed his private train at his Wonsan compound as recently as April 23.
Kim uses the train to travel because he fears being assassinated while in the air.
North Korea has officially denied having any cases of coronavirus, but reports that have leaked from inside the country suggest officials have privately admitted to citizens that the disease is spreading there.
Earlier this month a defector who escaped across the border into China tested positive for the virus, all-but confirming its presence there.
With that in mind, Kim's absence from major ceremonies should not be regarded as unusual, Unification Minister Kim Yeon-chul said today
'It is true that 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 cancelled because of coronavirus concerns,' he said.
He said there were at least two instances since mid-January where Kim Jong Un was out of sight for nearly 20 days.
US President Donald Trump said on Monday he has a good idea how Kim Jong Un is doing and hopes he is fine, but would not elaborate.
Japanese prime minister Shinzo Abe said he was aware of reports on Kim's health and he was was paying close attention to developments.
North Korea had cancelled some large events, and imposed a border lockdown and quarantine measures in an effort to prevent an outbreak of the coronavirus.
But 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 of monitoring group Korea Risk Group.
'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.
According to the Washington Post, the rumours over Kim's health have sparked panic buying in Pyongyang.
People have stocked up on rice, liquor, cigarettes, canned fish and electronics while helicopters have been flying low over the city, it is reported.
A source familiar with US intelligence reporting said it was entirely possible Kim had disappeared from public view to avoid exposure to avoid Covid-19.
The sighting of his presidential train in the coastal resort area of Wonsan could suggest he may be there or have been there recently.
But the source said that US agencies were also still considering the possibility Kim might be ill, even seriously.
While North Korean state media outlets have not reported on Kim's whereabouts since April 11, they have carried near-daily reports of him sending letters and diplomatic messages.
That suggests that he is still carrying out his duties, the South Korean minister said, although some experts say they are not necessarily conclusive.
The letters apparently sent in his name include a message of gratitude to workers in a tourist zone and a letter to South African president Cyril Ramaphosa.
'I agree with the South Korean government's assessment that there is no reason to think Kim Jong Un is not performing his duties,' said Rachel Minyoung Lee, a former North Korea intelligence analyst for the US government.
'That said, I would not read too much into letters signed by Kim Jong Un. I would guess that most of them are not written by him anyway.'
© Associated Newspapers Ltd.