North Korea's most influential newspaper again claimed Thursday that nobody has been infected with the new coronavirus so far in the country, saying measures will be stepped up to prevent the pandemic from spreading there.

If North Korea lets its guard down, that would trigger a "crucial crisis," said the Rodong Sinmun, the newspaper of the Workers' Party of Korea.

The official Korean Central News Agency said Sunday that a first suspected case of the novel coronavirus in North Korea had been detected, prompting leader Kim Jong Un to convene an emergency meeting of the ruling party.

Photo taken July 29, 2020, from South Korea's Ganghwa Island shows the suburbs of the North Korean border city of Kaesong seen on the other side of the Han River. A North Korean defector suspected of having been infected with the new coronavirus in South Korea has reportedly returned to the North by crossing the river. (Kyodo)

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A person, who defected to South Korea three years ago, is "suspected to have been infected with the vicious virus" after "illegally" returning to the North's border city of Kaesong, the news agency said.

But state-run media have yet to report whether the person has been definitely diagnosed as a COVID-19 patient.

KCNA said Kaesong has been "totally" blocked since Friday, while people who came into contact with the person and those who have traveled from the city in past five days have been put under quarantine.

Since earlier this year, North Korea has cut off traffic to and from its neighbors, China and Russia, amid the outbreak of the virus, which was first detected in the central Chinese city of Wuhan.