The FBI said on Wednesday it was investigating a report that tens of millions of drivers’ licenses belonging to people in the ​United States and Canada were being sold on the dark web.

On Tuesday, the ‌independent journalist Brian Krebs said he had discovered a dark web site, selling digital scans of millions of drivers’ licenses from people in the US and Canada. He said he confirmed the authenticity of the ​data being sold with nine people.

In a brief statement on Wednesday, the bureau ​said it was “looking into the incident” but could not comment “due to the ⁠ongoing nature of the investigation.”

The breach, if confirmed, could be one of the largest-ever exposures ​of government-issued identity documents in North America, creating risks of identity theft and fraud for ​tens of millions of people.

Krebs said he was alerted to the site after it was advertised on a Russian cybercrime forum, with his own driver’s license being offered as a free sample.

Krebs said the ​service, dubbed Nexus, claimed to have tens of millions of licenses for people in the ​US and Canada, as well as millions of other identification cards and travel documents and hundreds of ‌thousands ⁠of medical records.

Krebs said that the site appeared to be updating its database of stolen data in real time, indicating that it was being fed by a live breach.

Zach Edwards, a threat researcher at the cybersecurity company Infoblox, said the incident was unprecedented in terms ​of its sweep.

“There’s never ​been a breach ⁠of driver’s licenses at this scale,” said Edwards, who added that his own license was available for sale on the site. Edwards said ​that the ongoing nature of the breach “means that this attack created ​legitimate national ⁠security risks for high-profile individuals.”

Reuters could not establish the source of the stolen data. Krebs quoted a representative of New Orleans-based identity verification provider IDScan.net as saying that it was investigating the matter.

IDScan.net, ⁠which ​describes itself as providing “ID fraud prevention at scale,” did ​not return repeated messages from Reuters.

Krebs said the dark web site offering the driver’s license data vanished shortly after ​he published his report.