Secretary of State John F. Kerry said Thursday that U.S. diplomats remain “very much focused” on efforts to release Americans held in Iran, including a Washington Post journalist whose case is now in the hands of a top court.

The remarks by Kerry, during a stop in Bulgaria, came a day after Tehran’s chief prosecutor said Iran’s Revolutionary Court has the case of The Post’s Tehran bureau chief, Jason Rezaian, who has been detained since July.

The charges against Rezaian have not been made public, and he has been denied access to a lawyer. It was unclear whether the court was planning to further review the case or move toward trial.

Kerry said U.S. envoys constantly press for information on Rezaian and other U.S. citizens held in Iran while seeking their release. The disputes also could assume greater prominence as world powers and Iran continue talks on possible ways to monitor the country’s nuclear program.

“We are very much focused on each of these citizens,” Kerry said in Bulgaria’s capital, Sofia. “We are currently engaged in efforts to follow up on them.”

The Washington Post's Jason Rezaian has been detained in Iran since July. The charges against him have not been made public. (Zoeann Murphy/The Washington Post)

Rezaian’s brother, Ali Rezaian, repeated the family’s request that the journalist receive access to legal counsel and that the accusations against him be made public.

“While we are disappointed that the Iranian judiciary did not dismiss these as-yet-unspecified charges, we are encouraged by the fact that, with the case now squarely in the hands of the judiciary, it is moving through their legal process in a more timely and transparent manner,” Ali Rezaian said.

He added that it was the responsibility of Iran’s judiciary to “immediately grant Jason access to a lawyer and his case file, as he was assured when he was charged in December and has been required by Iranian law since July.”

On Wednesday, Iranian news agencies quoted Tehran prosecutor Abbas Jafari Dolatabadi as saying that Rezaian’s case had moved to the Revolutionary Court for “processing.”

The wording suggested that the court could study the case before moving toward a possible trial. The Revolutionary Court handles Iran’s most sensitive cases, including those involving security matters.

Rezaian, 38, was officially charged Dec. 6, but he does not know the exact allegations against him, other than that they pertain to purported “activities outside the bounds of journalism,” his family said in a recent interview.

Martin Baron, executive editor of The Post, said in a statement Wednesday: “We still do not know what ­charges the Iranian authorities have brought against our correspondent Jason Rezaian, but we hope the referral of his case to a Revolutionary Court represents a step forward toward Jason’s prompt release.

“This step gives Iran’s judiciary an opportunity to demonstrate its fairness and independence by determining that the charges­ are baseless. We call on Iran to make these charges public, to allow Jason access to a lawyer and to bring a swift and just resolution of a six-month-long nightmare that has been extremely difficult for Jason and his family.”

Rezaian has dual U.S.-Iranian citizenship.

State Department officials have said Kerry also has expressed concern for three other Americans in prison or otherwise unaccounted for in Iran. Among the three is Amir Hekmati, a Marine veteran who has been held by the country since August 2011.

Hekmati, who also has dual U.S.-Iranian citizenship, was captured while visiting his grandmother in Iran, his family says. Tehran has accused him of being a CIA spy, a charge that Hekmati and the U.S. government deny.

Morello reported from Sofia.