The Washington Post on Monday slammed the conviction of its reporter Jason Rezaian in Iran as an "outrageous injustice" and said it was working with his family and lawyer to prepare a quick appeal.

Rezaian, the US newspaper's Tehran correspondent and a dual Iranian-American citizen, was arrested in July 2014 and accused of spying, along with other crimes against national security. 

"Iran has behaved unconscionably throughout this case, but never more so than with this indefensible decision by a Revolutionary Court to convict an innocent journalist of serious crimes after a proceeding that unfolded in secret, with no evidence whatsoever of any wrongdoing," the paper's executive editor Martin Baron said.

Rezaian was tried in four hearings behind closed doors, the last of which was held in August.