WASHINGTON — The chairman of the Senate Judiciary Committee says the FBI is improperly restricting access to materials from its closed investigation into Hillary Clinton’s use of a private e-mail server.

In a letter sent Wednesday to the Senate’s security director, Iowa Sen. Chuck Grassley asked that unclassified portions of the FBI documents be provided to his staff.

The move appears to be an end run around strict restrictions imposed by the FBI, which warned members of Congress not to leak documents from its investigation involving the Democratic presidential nominee.

Congressional aides told The Associated Press that the investigative materials demanded by House Republicans are being kept in a secure room on Capitol Hill typically reserved for the nation’s most closely guarded secrets.