North Korea's Kim Jong Un declared victory in the battle against COVID-19 on Thursday, with the leader's sister revealing he had suffered from fever and vowing "deadly retaliation" against South Korea, which it blames for causing the outbreak.

Kim ordered a lifting of maximum anti-epidemic measures imposed in May, adding that North Korea must maintain a "steel-strong anti-epidemic barrier and intensifying the anti-epidemic work until the end of the global health crisis," according to a report by state news agency KCNA.

North Korea has never confirmed how many people caught COVID-19, apparently lacking testing supplies. It had instead reported daily numbers of fever patients, which totaled some 4.77 million, but has registered no new such cases since July 29.