TOKYO - Japan's health ministry said Thursday foreign materials were confirmed in some portions of the unused doses of Moderna Inc.'s COVID-19 vaccine and the use of around 1.63 million doses manufactured in the same production line has been suspended as a precaution, local media reported.

The Ministry of Health, Labor and Welfare said foreign substances have been confirmed since Aug. 16 at eight vaccination sites in the prefectures of Ibaraki, Saitama, Tokyo, Gifu and Aichi.

Japanese drugmaker Takeda Pharmaceutical Co., in charge of sales and distribution of the vaccine in the country, said it has yet to see any reports of safety concerns and has reported them to the ministry on Wednesday.

The size of foreign substances found in 39 vials is believed to be a few millimeters.

"To date, no safety or efficacy issues have been identified," Moderna told local media, adding it is "carefully assessing this matter and at this point does not have further comments on root causes."

The health ministry said the 1.63 million doses of Moderna vaccine were made in the same production line at the same time in Spain, and fall under three lot numbers -- 3004667, 3004734 and 3004956, which has already been handed out to 863 vaccination centers across the country.

The ministry said it believes the risk of safety issues is "not significant," but will ask each facility that received the doses not to use them.

Over 10 million doses have already been used in the country since the Moderna vaccine accepted approval for emergency use in May, according to the government.

The Japanese government signed a contract with Moderna to receive 50 million doses of the COVID-19 vaccine by the end of September. Currently people aged 12 and older can get shots of the vaccine.

Meanwhile, the health ministry revealed to public the lot numbers of the contaminated vaccines so that concerned individuals can check whether they received the potentially contaminated shots before the affected vaccine doses were suspended.

On similar abnormalities that may have been found in other countries, Moderna said it monitors and expeditiously assesses questions it received about the products from global markets, and local authorities will make their own decisions about disclosure of information following these assessments.

The problem was exposed to view at a time when Japan is struggling to control a peak in COVID-19 infection cases, as the government declared a plan on Wednesday to put eight more prefectures under its COVID-19 state of emergency.

While vaccinations against COVID-19 are under way in Japan, the highly contagious Delta variant has brought the surge of daily confirmed cases in many parts of the country.