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TOKYO (AP) — Japan on Wednesday confirmed its first known local transmissions of the new omicron variant of the coronavirus in Osaka, a sign it is already making its way in the country.

The family of three in Osaka had no record of traveling overseas and their infections could not be traced, Osaka Gov. Hirofumi Yoshimura said.

The three are the first known cases of community transmission of the highly infectious omicron variant in Japan, Yoshimura said. “I believe they only happened to be detected and we must take steps on the assumption that there already are other cases of community transmission,” he said.

Yoshimura said current restrictions on eateries in Osaka will remain in place, including a limit of four people per table for a maximum of two hours, to minimize risks during the yearend holiday season, when coronavirus infections surged last year.

More than 100 omicron cases have been identified in mainland Japan, but all involved people who tested positive upon entry at airports or those linked to them, government officials have said.

Health Minister Shigeyuki Goto, responding to the confirmation of the Osaka cases, said the government will do its utmost to prevent a further spread of the variant.

Concerns are also growing on Japan’s southern island of Okinawa, where a large virus cluster has developed at a U.S. military base. Several Japanese employees at the base have tested positive for the omicron variant, raising suspicion they might be linked to the cluster on the base.

As of Wednesday, 215 Marines recently transferred from the U.S. to Camp Hansen on Okinawa have tested positive for the coronavirus, but it is not known if they are omicron cases, Foreign Minister Yoshimasa Hayashi said.

Hayashi said he urged the commander of U.S. Forces Japan, Lt. Gen. Ricky Rupp, to conduct genomic analyses of the samples, step up anti-virus tests and other measures and prohibit troops from leaving the base to prevent the spread of the virus into the community.

Hayashi said the U.S. military has agreed to cooperate with Japan in testing cases for the omicron variant and share results with Japanese authorities.

Japan eased its border controls in November, but quickly reinstated a ban on most new foreign entrants after omicron was first identified in South Africa.

Prime Minister Fumio Kishida said Tuesday that he plans to keep the border controls, among the world’s most stringent, in place until more details about the omicron variant are known.

Kishida said Japan is also tightening quarantine rules for those who come in close contact with omicron patients, requiring 14 days of isolation at designated facilities instead of the previous self-isolation at home.

He also announced plans to accelerate booster shots of COVID-19 vaccines, which started with medical workers in December.