The U.S. Embassy in Tokyo issued a warning Monday about foreign residents being stopped and searched by Japanese police in what it said were suspected to be "racial profiling incidents.”

The unusual move by the embassy of Tokyo’s only formal ally came after Japan closed its borders to newly arriving foreign nationals amid concern over the omicron variant, just weeks after beginning a cautious reopening. The closure was backed by almost 90% of respondents to a media poll over the weekend.

The alert posted by the Twitter account of the American Citizen Services section of the embassy warned that U.S. citizens should carry proof of their immigration status and notify their consulate if detained. The alert added that several foreigners "were detained, questioned, and searched.”

Chief Cabinet Secretary Hirokazu Matsuno dismissed the concerns and said at a news briefing that police questioning in the country is not based on nationality or race.

The number of foreign citizens living in Japan fell by 2% to 2.8 million in June, compared with a year earlier, according to the Justice Ministry. American citizens made up less than 2% of the total, at nearly 54,000. Entry by foreign tourists, businesspeople and students is currently banned under coronavirus restrictions, although foreigners with resident status are currently permitted to re-enter.