Staff disinfecting Pyongyang station in an anti-epidemic prevention campaign to curb the current coronavirus disease (COVID-19) health crisis in Pyongyang, North Korea. North Korean leader Kim Jong Un has ordered nationwide lockdowns and mobilized troops to tackle the pandemic since the country first disclosed the COVID-19 outbreak last week. EPA-EFE/KCNA EDITORIAL USE ONLY 
Four fever cases "suspected of being infected with malignant epidemic" were reported from Ryanggang Province near the border with China on Tuesday, prompting authorities to immediately lock down the area and mobilise medical teams, the official KCNA news agency said, citing the State Emergency Epidemic Prevention Headquarters.
But a detailed analysis of the nationwide epidemic situation showed that there have been no Covid-19 cases since the country's outbreak ended early this month, KCNA said.
Still, authorities have dispatched epidemiological, virology and test experts to the area to investigate the cause of the fever cases, while imposing measures to prevent their spread, it said.
Authorities are "taking steps to trace all persons, who connected with the suspect cases, and persons going to and from the relevant area and keep them under strict medical observation," KCNA said.
After North Korea declared victory over Covid-19, it blamed South Korea for causing the outbreak and vowed "deadly retaliation" against it. South Korea denied the claim as groundless.
Officials have since scrapped a face mask mandate and other restrictions including limits on the use of public facilities except in border regions.
North Korea has never confirmed how many people caught Covid, apparently because it lacks the means to conduct widespread testing.
Instead, it reported daily numbers of patients with fever, a tally that rose to some 4.77 million. But it said it had registered no new such cases since July 29.
By Hyonhee Shin
(Reporting by Hyonhee Shin; Editing by Kim Coghill)