A Washington Post reporter who has been imprisoned in Iran for more than four months appeared in a Tehran court Saturday where he was officially charged, but specifics of the charges are not yet known, a source familiar with the case told The Post.

The reporter, Iranian American Jason Rezaian, a dual citizen and The Post's bureau chief in the Iranian capital since 2012, was initially arrested July 22, but Saturday's charges were the first brought against him. Rezaian reportedly spent 10 hours in court while a judge reviewed his case.

Rezaian's family hired a lawyer, however the lawyer has not been allowed to visit, according to The Post.

According to The Post, it could take a month for a trial to be set, at which point Rezaian's lawyer will likely be allowed to make contact and review the charges, the source said.

"The Iranian government has never explained why Jason was detained or why he has been held for more than four months without access to a lawyer," Washington Post Executive Editor Martin Baron said in a statement. "Jason is an American citizen who was acting as a fully accredited journalist. If he has indeed been charged, we know that any fair legal proceeding would quickly determine that any allegations against him are baseless."

During the ongoing nuclear talks with Iran, the U.S. State Department has repeatedly and directly asked Iranian officials for the release of Rezaian along with other Americans imprisoned in the country.

"Iranian government continues to deny our repeated requests for Consular Access to Jason by our Protecting Power, the Swiss, so we are unable to check on his condition or ensure adequate legal representation," U.S. Secretary of State John Kerry said in a statement issued to The Post on Sunday.

"Jason poses no threat to the Iranian government or to Iran's national security. We call on the Iranian government to drop any and all charges against Jason and release him immediately so that he can be reunited with his family."

"Likewise," Kerry continued, "we again call for the release of U.S. citizens Amir Hekmati and Saeed Abedini, and ask for the Iranian government's cooperation in locating Robert Levinson, so that all may be returned to their families."