Iranian authorities accused a group of minority Arabs with the 2011 deaths of police officers during a protest. Some were later thought to have been convicted of "sowing corruption" and other charges that carry the death penalty in Iran.
Sources close to the accused told Human Rights Watch some of the men were likely executed and others had been transferred to undisclosed locations ine Iran.
Joe Stork, deputy Middle East director at Human Rights Watch, said Tehran was obligated to keep family members aware of their fate.
"Even when someone has been convicted of a serious crime, it doesn't mean the person's family should be left in the dark," said Stork in a statement from New York. "The authorities need to deliver the bodies of those executed to allow proper burial."
The British government this week criticized Iran's record after human rights defender Abdolfattah Soltani was sentenced to 13 years in prison on charges of distributing "propaganda against the state." In 2003, he helped set up the Center for Human Rights Defenders with Nobel Peace Prize laureate Shirin Ebadi.
Newt Gingrich fires back at Mandela backlash
Campus cop fatally shoots Texas student during traffic stop