TOKYO -- Japan will suspend entry into the country by foreign nationals starting Tuesday, citing the emergence of the omicron variant of COVID-19.

The government lifted its entry ban earlier this month for foreign business travelers and students but has reversed course in hopes of preventing another wave of infections.

Prime Minister Fumio Kishida told reporters on Monday that the government is dealing with the threat of the omicron variant "with a strong sense of crisis."

All Japanese nationals, vaccinated or not, returning to the country will have to quarantine for 14 days, instead of the current three or 10 days for the vaccinated. Those returning from Angola and other countries where the variant has been detected will be placed in strict quarantine at designated facilities.

The measures are expected to last for at least one month, serving as a precaution until more information on the omicron strain becomes available, the government said.

As a result, only Japanese nationals and foreigners with special permission can enter Japan.

Hirokazu Matsuno, the chief cabinet secretary, said at a news conference that no cases of the omicron strain had been confirmed in Japan, as of Monday morning.

This marks a major reversal of Japan's policy. After infection numbers plummeted, the government on Nov. 8 approved the entry of foreign business travelers, students and technical interns. Just last Friday, the government started allowing up to 5,000 people to enter each day. But from Wednesday, that number will shrink to 3,500. The country remains closed to tourists.

As of now, those arriving from South Africa and eight other countries are being asked to stay at designated facilities for up to 10 days.

Angola will be added to the list from Tuesday, and 13 other countries and regions will join the list from Wednesday.

Travelers from Australia, Germany, France, the Czech Republic and Hong Kong will have to stay in designated facilities for three days. Those traveling from Israel, the U.K., Netherlands and Italy will have to stay for six days.

The minimum quarantine period for entrants was shortened to three days for short-term stays for business, provided a detailed description of the person's whereabouts in Japan is submitted. The quarantine for technical interns and foreign students was 10 days for those who are vaccinated.

The government has decided to suspend these measures in light of the new variant. Omicron was designated a "variant of concern" by the World Health Organization on Friday.

Its emergence has rattled markets, triggered travel bans and put vaccine makers on alert. Cases of the Omicron virus have already been found in Germany, Italy, Australia, the Netherlands and other countries outside Africa. Israel has decided to ban all foreigners from entering the country. The U.S. and Europe have also announced restrictions on travel from South Africa and other countries.

To minimize the chances of new outbreaks in Japan, the government already had in place strict conditions on the entry of new business travelers into the country, such as requiring that they be strictly overseen by their host company or organization.