North Korea's No. 2 leader has visited the border city of Kaesong to inspect antivirus efforts, state media reported Thursday, after leader Kim Jong-un sealed off the town over virus fears following the return of a defector from South Korea.

On Sunday, North Korea said that it has put Kaesong on lockdown, claiming that a "runaway" defector suspected of COVID-19 infection recently came back from the South. Seoul later said a North Korean defector is believed to have swum across the border but doubted he had contracted the virus.

Choe Ryong-hae, president of the Presidium of the Supreme People's Assembly, visited Kaesong and inspected emergency antivirus efforts underway in the town, according to the Korean Central News Agency.

Choe held a meeting with local officials and instructed them to make sure that food and medical supplies are provided to residents in need and that disinfection and other antivirus measures should be strictly carried out as required, KCNA added.

His trip to Kaesong appears aimed at emphasizing the importance of antivirus efforts and urging people to stay vigilant amid growing fears that the coronavirus could break out in the border town and spread to the rest of the country.

State media, however, said Thursday there has been no COVID-19 infection in North Korea, the first mention that the country remains virus-free since Pyongyang put Kaesong on lockdown following the return of the defector showing virus symptoms.

"There has not been even a single case of new coronavirus infection so far in our country," the Rodong Sinmun, the official newspaper of the North's ruling party, said in an article.

As of Thursday, North Korea has not reported any confirmed infection case to the World Health Organization and other relevant international organizations.

It is still unclear whether the report means the defector with virus symptoms eventually tested negative for the disease or not.

State media earlier said the defector has been put under "strict" quarantine after several medical checkups produced an "uncertain result."

North Korea has said it is coronavirus-free, but outside observers have questioned the claim since it has a long and porous border with China hard-hit by the virus and is known to have underequipped and understaffed infrastructure to cope with such highly contagious diseases.

Despite its claim to be free of the virus, the North has taken relatively swift and drastic measures, shutting down its borders since late January and tightening quarantine measures. Pyongyang has called its fight against the virus a "political matter" that will determine the fate of the country. (Yonhap)