The top U.S. military commander in South Korea told reporters on Friday he is “fairly certain” the coronavirus pandemic has already entered the DPRK, despite Pyongyang’s denials that the country has had any cases so far.

The comment, from the UN Command and U.S. Forces Korea (USFK) commander General Robert Abrams, comes as nations around the world — including many with highly advanced healthcare systems and wealthy economies — are fighting to contain the spread of a virus that has already sickened tens of thousands and killed at least 5,000 people.

Unconfirmed reports of infections have trickled out of North Korea for weeks, but Pyongyang has so far reported no cases of the contagious virus, also known as COVID-19.

“You’ve seen the public statements by North Korea,” Abrams said in a video-conference at the Pentagon, according to South Korea’s Yonhap News Agency. “They claim that they have no COVID-19 cases.”

“It is a closed off nation so we can’t say emphatically that they have cases, but we’re fairly certain they do,” he said.

“What I do know is that their armed forces had been fundamentally in a lockdown for about 30 days and only recently have they started routine training again,” Abrams continued. “As one example, they didn’t fly an airplane for 24 days.”

The DPRK conducted its first military drills of the new year in late February, followed by three more rounds of drills and missile tests in recent weeks — all reportedly overseen by Kim Jong Un, according to North Korean state media. The latest drills reportedly occurred on Thursday.

For their part, the U.S. and South Korea last month announced they had canceled a scheduled round of military exercises because of the coronavirus outbreak.

Even as the DPRK continues to say it does not have any coronavirus infections within its borders, its neighbors have been some of the worst-hit countries in the world.

The outbreak began in China, where the vast majority of the world’s known infections have been found. South Korea has reported thousands of cases as well.

North Korean state media has tracked the South’s infection numbers while boasting about its own all-out “anti-epidemic” measures.

“Officials of the Party and power organs and working people’s organizations and those in the fields of public health and anti-epidemic control across the country have boosted the hygienic information service about the worldwide spread of COVID-19 and preventive and treatment measures among the people, so that they should never feel relieved for having no COVID-19 case in the DPRK,” said one recent article in the official Korea Central News Agency (KCNA).

Rodong Sinmun, the ruling Workers’ Party’s daily newspaper, wrote that officials in the North’s Jongju City are “positively waging hygienic information services so that inhabitants wear masks with a sense of duty, frequently wash their hands and observe the rules of health.”

The DPRK has also reportedly quarantined thousands of people, apparently as part of an effort to prevent the disease from spreading. Some have already been released from quarantine.

Despite the projections of confidence, however, North Korea is known to have one of the worst public health systems in the world — one that is severely ill-prepared to deal with a contagious disease epidemic.

One major public health study last year found that the country ranked last among nations in its capacity to handle an outbreak.

Humanitarian workers with experience in North Korea told NK News recently that the country is woefully lacking in supplies — and even if the equipment is there, many medical facilities do not have reliable sources of electricity, water, or heat.

Amid the coronavirus outbreak, Russia and China may be providing some direct aid to the North — Moscow claims to have sent 1,500 test kits to the country — and international aid groups have received permission from the UN to bypass sanctions and bring otherwise-banned supplies into the country, but it remains unclear how much of that Pyongyang has actually allowed in.