HRW's call for a halt to the executions comes after reports Iranian authorities had executed on June 17 four Arab men charged with terrorism-related activities, the human rights group said in a news release.
A friend of three of the men -- Hadi Rashedi, 38, Hashem Shaabani, 32, and Mohammad-Ali Amouri, 34 -- told HRW they are at "imminent risk of execution." They had been convicted behind closed doors of terrorism charges for alleged membership in an armed Arab separatist group and participation in what the human rights group called "armed activities."
Two Iranian-Arab brothers -- Seyed Mokhtar, 25, and Seyed Jaber Alboshokeh, 27 -- also have been issued death sentences, the release said.
The five men, all arrested in February 2011, are from Iran's majority-Arab Khuzestan province.
"What we are witnessing today in Iran's Khuzestan province is state-sanctioned killing that, by many accounts, is aimed at silencing voices that are critical of the government's policies in the region," Sarah Leah Whitson, Middle East director at Human Rights Watch, said in the news release.
Because of an information blackout and secrecy surrounding security trials in the Khuzestan province, there's little information about the evidence against the five men except for televised confessions, HRW said.
"The judiciary has put forth no public evidence suggesting that these men should spend one more day in prison, let alone hang from the gallows," Whitson said. "The lack of transparency surrounding these men's convictions and sentences is just one more reason why these execution orders should be quashed."
HRW said it has documented numerous cases in which Iranian authorities have used torture that has led to false confessions.
The release said since May 2011, authorities have executed at least 11 Iranian-Arab men and a 16-year-old boy in Karun prison for their alleged links to groups involved in attacking security forces. Rights activists had previously said at least six other people had been tortured to death in custody in connection with anti-government demonstrations in Khuzestan province in April 2011 and 2012.