TOKYO (Reuters), -The U.S. military bases at Japan implemented stricter measures Thursday to combat an increase of COVID-19 patients after the government expressed serious concern about the spread.

U.S. Japan’s forces stated that it will “enforce more stringent mitigation steps in an effort to stop virus transmission.”

It stated in a press statement that the measures included a requirement for U.S. military personnel not to wear masks on base, and stricter testing mandates.

Yoshimasa Hayashi, the Japanese foreign minister, requested that U.S. Secretary Of State Antony Blinken restrict U.S. military personnel from leaving bases. Hirokazu Mattsuno, chief cabinet secretary, told reporters.

Matsuno stated that the Japanese government is “gravely worried” about COVID infection at U.S. military bases.

Okinawa’s southern prefecture, which hosts 70% of U.S. military installations in Japan, is leading the country in new infection and has requested quasi-emergency actions from the central government.

Japan made it impossible for foreign tourists to enter Japan after Omicron, a World Health Organisation variant of concern, was identified.

However, the U.S. military was able to allow staff into and out of the country in a separate quarantine and testing regime. Residents living near the bases have expressed concern about the possibility of spreading the virus to others.

Okinawa’s new COVID-19 cases surpassed the number of the prior day by more than twofold on Wednesday. This surge, Governor Denny Tamaki claims was the result Omicron.

The U.S. Marine Corps Station Yamaguchi in western Japan reported Wednesday that it had discovered 115 additional cases. This is in addition to the 182 previously found the day before.