SEOUL, South Korea — North Korea has announced that it will not accept any foreign tourists beginning Friday because of fears of the Ebola virus, three agencies that take tourists to the isolated country said on Thursday.

The news came as the country said it was stepping up inspections and quarantine measures at its main airport, borders and ports to guard against the spread of the deadly virus, which has killed thousands of people in the latest outbreak.

“Three days ago, they said that anybody who’s been to West Africa would have to provide a doctor’s certificate stating that they don’t have Ebola,” said Gareth Johnson of Young Pioneer Tours, a travel operator based in China. “And then today, they just said no foreign tourists at all.”

Mr. Johnson said that he had received the notice from his North Korean partners and that one of his tour guides who was visiting the North with a group of foreign tourists had also confirmed it through the authorities there. Mr. Johnson said his company had to cancel its plans to take a group of 20 tourists to the North on Monday.