North Korea had its military forces on lockdown for about 30 days and in one instance did not fly a plane for 24 days, even though it has not confirmed any cases of coronavirus, the head of U.S. forces in South Korea said on Friday.

"Their armed forces has been fundamentally on lockdown for about 30 days and only recently have they started routine training again," General Robert Abrams told reporters at the Pentagon, adding that he was fairly confident the country had cases of the virus.

North Korea, sandwiched between China and South Korea, has not confirmed any coronavirus cases but has stepped up border checks and imposed quarantine measures.