The announcement came as the government imposed new virus restrictions in three regions, including Okinawa, that host major US bases or are near them.

Many Japanese officials believe the recent Covid-19 clusters originated from infected American service members coming into contact with local residents.

On Friday, Japan's foreign and defence ministers had warned their US counterparts to implement stricter anti-pandemic rules for US troops.

"Movement of USFJ (US Forces, Japan) personnel outside of (US military-related) facilities and areas will be restricted to essential activities only," read a joint statement from the Japanese government and the USFJ issued late Sunday.

Service members will also have to wear masks when they are outside of their homes, it added.

In mid-December, the US military reported clusters of cases among its members in a southern region of Okinawa, which subsequently saw a sharp rise of cases in the local community.

Japan has imposed strict border control measures, such as quarantine and frequent testing, on those who enter the country from abroad.

But the same rules have not applied to US service members, with Foreign Minister Yoshimasa Hayashi saying that until recently incoming troops were not even tested for the virus on arrival, or required to quarantine.

Hayashi had had repeated online meetings with US Secretary of State Antony Blinken in recent days, urging Washington to restrict US forces' movement.

Okinawan officials say the US military reported 998 infections on-base between December 15 and January 5.

The island region hosts the bulk of some 54,000 US troops in Japan.