The Washington Post said Monday allegations that its Tehran reporter was engaged in espionage were "absurd" as it renewed its plea for Iran to free the journalist.
The US daily reacted to a report saying Jason Rezaian was being charged with giving economic intelligence to the Central Intelligence Agency.
Washington Post executive editor Martin Baron said in a statement in the daily that "any charges of that sort would be absurd, the product of fertile and twisted imaginations."
Baron added, "We are left to repeat our call on the Iranian government to release Jason and, in the meantime, we are counting on his lawyer to mount a vigorous defense."
Rezaian, a dual US and Iranian citizen, was detained by Tehran in July 2014, but no charges were reported until the Fars news agency said Sunday he would be tried on charges of espionage and crimes against national security.
Fars, considered to be linked to the Revolutionary Guards, said the journalist was accused of "selling Iran's economic and industrial information" to US intelligence.
The news comes just days after Washington and Tehran reached a landmark agreement which would curb Iran's nuclear program and potentially lift economic sanctions.
The United States and Iran have long been foes. Diplomatic ties were snapped in the wake of the 1979 Iranian Revolution and the subsequent hostage crisis in Tehran, when US diplomats were held hostage by militant students for 444 days.