The FBI has taken possession of thumb drives containing Hillary Clinton’s emails, some of which have been deemed to contain highly sensitive classified information, according to a U.S. official briefed on the matter.

The official was not authorized to be quoted publicly and spoke on condition of anonymity.

Clinton’s lawyer, David Kendall, turned over the emails after the FBI determined that he could not remain in possession of the classified information, the official said. The State Department previously had said it was comfortable with Kendall keeping the emails at his Washington law office.

The news came as Sen. Charles Grassley said two of the emails, which traversed Clinton’s insecure home email server, were deemed “Top Secret, Sensitive Compartmented Information,” which is among the government’s highest classifications.

Grassley said the inspector general of the intelligence community had reported the new details about the higher classification to Congress on Tuesday.

Those two emails were among four that had previously been determined by the inspector general of the intelligence community to have been classified at the time they were sent. The State Department disputes that the emails were classified at the time.

The U.S. official said the FBI recovered at least two thumb drives containing the emails from Kendall. The drives contain around 30,000 emails that Clinton deemed work-related and turned over to the State Department. She destroyed thousands of others that she said were not work-related.

The inspector general for the Intelligence Committee told Congress that potentially hundreds of classified emails are among the cache that Clinton provided.

Former Secretary of State Clinton, a Democrat running for president, has faced criticism over her use of a private email address and home server for official business.

Her campaign and Kendall did not immediately respond to a request for comment.

The FBI is looking into the security of the Clinton email arrangement. There is no evidence she used encryption to shield the emails from foreign intelligence services or other prying eyes.

(AP)