Washington Post reporter Jason Rezaian, shown at the newspaper in this Nov. 6, 2013, photo, has been officially charged in Tehran after being detained for months, a source familiar with the case said. (Zoeann Murphy/AP)

Jason Rezaian, a Washington Post reporter who has been detained in Iran for more than four months, was officially charged Saturday in a day-long proceeding in a Tehran courtroom, according to a source familiar with the case.

The specifics of the charges are still unknown, at least to those not present in the courtroom. The court appearance came two days after word arrived in the West that Rezaian’s detention has been extended until mid-January because the investigation against him is continuing.

The charges were the first lodged since Rezaian, an Iranian American who holds dual citizenship, was arrested July 22. His family has hired a lawyer for him, but the attorney has not been permitted to visit him. The State Department has repeatedly raised the case of Rezaian, and other Americans jailed in Iran, during lengthy talks with the Tehran government about a deal to curb Iran’s nuclear capacity and ease international sanctions.

The source said Rezaian spent about 10 hours in court Saturday while a judge reviewed his case. A translator accompanied Rezaian, who does not read Farsi, said the source, speaking on the condition of anonymity because of the sensitivity of the case. Rezaian signed a document saying he understood that he was being charged, the source said.

The proceedings appear to dash any hope that Rezaian could be freed in the near future. It could take as long as a month for the charges to be delivered to the full court, which would then set a trial date, the source said.

Theoretically, at that point Rezaian’s attorney would be permitted to review the charges and might be allowed to speak with his client, the source said.

Secretary of State John F. Kerry, in a statement issued early Sunday, said that the “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.”

Kerry said he had “repeatedly raised Jason’s case, and the other cases of detained or missing U.S. citizens, directly with Iranian officials.

“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,” Kerry said.

There are divergent views in Iran about the arrest of Rezaian, who has been The Post’s bureau chief in Tehran since 2012.

In a recent interview with France 24 television, the secretary of Iran’s Human Rights Council, Mohammad Javad Larijani, said he hoped that Rezaian’s case will be presented to the court “as soon as possible. . . . Let us hope that this fiasco will end on good terms.”

Washington Post Executive Editor Martin Baron expressed outrage Saturday over Rezaian’s continued detention. Rezaian’s family is concerned about the effect the imprisonment may have on his health, as he has high blood pressure, multiple infections, back issues and emotional stress caused by his lengthy time in Tehran’s notorious Evin prison.

“We are dismayed and outraged by reports that Jason ­Rezaian, The Post’s correspondent in Iran, has now been charged with unspecified crimes,” Baron said in a statement.

“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. 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.”

Rezaian was arrested with his wife, Yeganeh Salehi, also a journalist, but she was released on bail early in October. She is the only one who has been permitted occasional visits with him.