DUBAI/WASHINGTON (Reuters) - A court in Iran has convicted Washington Post reporter Jason Rezaian, Iran's ISNA news agency said on Sunday, but the U.S. newspaper said Tehran was working a political angle by not disclosing details.

ISNA quoted judiciary spokesman Gholamhossein Mohseni Ejei as saying the California-born Rezaian, the paper's Tehran bureau chief, had 20 days to appeal the verdict. Rezaian was arrested in July 2014. He was accused of espionage.

"He has been convicted. ... But I don't have the details of his verdict," the news agency quoted Ejei as saying.

The case has been a sensitive issue for Washington and Iran, and Sunday's announcement did little to resolve it.

State Department spokesman John Kirby said the United States was monitoring the case closely. "We continue to call for all charges against Jason to be dropped and for him to be immediately released," Kirby said earlier.

Iran has accused Rezaian, 39, of collecting confidential information and giving it to hostile governments, writing a letter to U.S. President Barack Obama and acting against national security. The Post has dismissed the charges as absurd. The final hearing in his trial was on Aug. 10.

Earlier, Ejei told a televised news conference that a ruling had been issued but did not say that Rezaian was convicted.

'VAGUE AND PUZZLING'

Washington Post Executive Editor Martin Baron said that that statement from Tehran was "vague and puzzling," and Post foreign editor Douglas Jehl said the vague nature of that announcement showed Rezaian's case was not just about espionage but that the reporter was a bargaining chip in a "larger game."

"It's increasingly clear that the final decision about how Jason's case will be handled will be made by political authorities, not by judicial ones," Jehl told Reuters.

Rezaian's brother Ali had noted on Friday that his brother had been imprisoned for 444 days - the same length of time that American embassy staff were held after the 1979 seizure of the U.S. Embassy in Tehran.

In a statement, he said Sunday's initial announcement "follows an unconscionable pattern by Iranian authorities of silence, obfuscation, delay and a total lack of adherence to international law, as well as Iranian law."

Iranian parliament speaker Ali Larijani hinted last month at the possibility that Rezaian could be freed in exchange for Iranian prisoners in the United States, but officials have played down the possibility of such a swap.

Two other U.S. citizens - Christian pastor Saeed Abedini and Amir Hekmati, a former U.S. Marine Corps sergeant - also are being held in Iran. Robert Levinson, a private investigator, disappeared there in 2007.

Their cases have been raised in subsequent talks, including between Iranian Foreign Minister Javad Zarif and U.S. Secretary of State John Kerry when they met during the U.N. General Assembly in New York last month. No progress was announced.

(Reporting by Sam Wilkin in Dubai and Bill Trott in Washington; Editing by Kevin Liffey, Howard Goller and Grant McCool)