Germany indicated on Friday it is concerned about potential attacks on its mass coronavirus vaccination centers.

The country is setting up six mass vaccination cites in Berlin ahead of the European Medicines Agency’s (EMA) approval of a vaccine, the Associated Press reports.

The EMA said on Tuesday that Pfizer and German company BioNTech filed for conditional approval of their vaccine candidate. The U.K. approved the vaccine for emergency use on Wednesday.

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Albrecht Broemme, who was tasked with setting up the agency, said security details still need to be resolved, according to the AP. He plans to have “intense conversations” with police and security firms about protecting the centers, though he acknowledged that no concrete threat has been made.

“With the centers it’s indeed possible that people opposed to vaccination or others willing to use violence might say ‘Let’s set this on fire because we think vaccinations are stupid,’” Broemme reportedly said.

Markus Lammert, a spokesman for Germany’s Interior Ministry, told reporters that security agencies were alerted to the issue, but he is not aware of any “concrete threat scenario.”

“In any case, we can’t provide information about operational details and facts,” Lammert said.

People have staged regular protests in Germany against the country’s coronavirus restrictions, arguing that they infringe on their rights. Opponents of the restrictions overlap with members of anti-vaccination groups who claim that COVID-19 vaccines will be compulsory.

The EMA’s Committee for Human Medicinal Products is expected to complete its review of Pfizer’s vaccine by Dec. 29. The committee is also expected to finish a review of Moderna’s vaccine by Jan. 12.