Human Rights Watch called Thursday for transparency from Iraq over its promised investigation of alleged abuses, including executions of civilians, by its forces during the recapture of Fallujah from the Islamic State group.
The New York-based watchdog said that since mid-June it had asked repeatedly for information from Baghdad over what it was doing to investigate the allegations, but not even basic details were provided and the inquiry was "mired in secrecy."
"Failing to hold fighters and commanders accountable for grave abuses bodes very badly for the looming battle for Mosul," HRW's deputy Middle East director, Joe Stork, said in a statement, referring to the last IS-held city in Iraq.
"Serious investigations and prosecutions are essential to provide justice to victims and their families, and to deter atrocities by government forces," Stork said.
At the end of last month, Iraqi forces recaptured Fallujah, a city 50 kilometres (30 miles) west of Baghdad, in a major setback for IS.
But the United Nations human rights chief Zeid Ra'ad Al Hussein said earlier this week that there was strong evidence that Ketaeb Hezbollah, one of the main militias that fought alongside security forces in the operation, carried out atrocities.
The Iran-backed militia may have executed dozens of civilians and kidnapped hundreds more, the UN said, citing witness testimony.
Prime Minister Haider al-Abadi responded to allegations of abuses during the operation by promising to investigate and prosecute all such cases.
But HRW said neither his office nor other officials "could provide any information about the purported investigations, including whether anyone has been arrested and charged."
IS overran large parts of the Sunni Arab heartland north and west of Baghdad in 2014, and Iraq turned to powerful Shiite militias to help halt the jihadists and later push them back.
The militias have played a key role in the fight against IS, but have also been repeatedly accused of abuses against civilians that have undermined the government's efforts to win back support in Sunni areas.