North Korean leader Kim Jong-un in a letter to President Moon Jae-in on Wednesday asked for help in combating coronavirus, fueling speculation that the outbreak in the North is worse than previously thought.

North Korea has claimed that it does not have a single confirmed case of infection, but there are rumors that the virus is spreading quickly there.

The state-run Rodong Sinmun daily said on Sunday that almost 7,000 people "are in self-quarantine and under medical monitoring."

One researcher at a state-run think tank here said, "North Korea revealed the number of quarantined subjects, because it's feeling the limitations of its medical capacity and wants help from the international community."

The North has sealed its borders, but it was apparently too late because the virus spread when North Korean workers returned from China en masse at the end of last year.