Japan’s Ministry of Health, Labour and Welfare suspended the use of more than 1.6 million doses of Moderna’s Covid-19 vaccine Thursday following reports of contaminated vials at multiple vaccination sites there.

Takeda Pharmaceuticals, which distributes the vaccine in Japan for Moderna, said it notified the ministry after several vaccination sites reported an unspecified foreign object found in one specific lot.

“We requested that Moderna, the product owner and manufacturer, conduct a thorough investigation to determine the precise root cause of the issue,” Takeda said in a statement.

Takeda also said that it is not aware of any “significant safety concerns” stemming from the contaminated doses.

Moderna said it’s been notified of the problem and is looking into it.

“The company is investigating the reports and remains committed to working expeditiously with its partner, Takeda, and regulators to address this,” Moderna wrote in a statement.

Japan’s chief cabinet secretary, Katsunobu Kato, told reporters Thursday that contaminated doses were administered to an unknown number of Japanese residents, though there have been no reports of ill effects, according to the New York Times.

All of the contaminated vials were made at manufacturing sites in Spain. It is still unclear if other countries besides Japan have been affected, though the European Medicines Agency said it’s also investigating the issue.

“EMA is investigating the matter and has requested the marketing authorisation holder to provide information on any potential impact on batches supplied to the EU in addition to details on the ongoing root cause investigation,” the agency said in a statement to Reuters.