Iran-backed forces in Iraq have warned they will not remain silent over an alleged US strike that they said killed 22 of their members across the border in Syria last week. Washington denied accusations by Damascus and Iraq's Shiite militias that it was behind the attack — which came amid escalating tensions between the US and Iran following President Donald Trump's decision to withdraw from the 2015 nuclear agreement. "To the Americans we say … we will not be quiet about this attack," senior Popular Mobilisation Forces (PMF) commander Jamal Jaafar Ibrahimi, known by his nom de guerre Abu Mahdi Al Mohandes, said in a video message late Sunday. The commander, one of Iran's most powerful allies in Iraq, said fragments of the missiles used in the strikes proved to be American. Mr Ibrahimi formerly head the Kataib Hezbollah militia, an Iran-affiliated group in Iraq The brigades hit last week are associated with Kataib Hezbollah. The Iraqi military said that none of its troops guarding the Iraq-Syria border had been hit in the air strike. "Forces hit by the air strike have not make any contact nor did they co-ordinate their presence there with Iraq's Joint Operations Command," a military statement said. Iraq regularly conducts air strikes against ISIS positions in Syria but does not have a troop presence across the border. The PMF was integrated into Iraq's state security structure after they assisted the military in defeating ISIS. The battles left cities in formerly ISIS-held territory severely damaged and displaced millions of civilians. Human Rights Watch on Monday accused Iraqi security forces of preventing families from returning home to Anbar province. “Families displaced since years by fighting with ISIS in Anbar are being prevented from returning home in a campaign of collective punishment, Iraqi authorities do not intervene, condemn, or help families go home,” Belkis Wille, HRW senior researcher, said on Twitter. The families, from the Saada tribe whose members have been accused of affiliating with ISIS, were taken to camps for displaced people in Anbar after being blocked from returning in late February and again in early June, the watchdog said. “It is unacceptable for soldiers to arbitrarily block residents from going home, in direct contradiction to the central government’s orders to facilitate safe and voluntary returns," said Lama Fakih, HRW's deputy Middle East director.