WASHINGTON — The U.S. filed new charges Thursday against Wikileaks founder Julian Assange, accusing him of placing the United States at risk of serious harm by publishing thousands of secret and classified documents, including the names of confidential sources for American armed forces.

In an 18-count, superseding indictment, Justice Department prosecutors allege that Assange directed former Army intelligence analyst Chelsea Manning in one of the largest compromises of classified information in U.S. history.

The case presents immediate questions about media freedom, including whether the Justice Department is charging Assange for actions — such as soliciting and publishing classified information — that journalists do as a matter of course.

Department officials said Thursday they believe Assange strayed far outside First Amendment protections.