US Secretary of State Rex Tillerson says it's time for Iranian-backed militias who helped Iraq defeat Islamic State to "go home" after a rare meeting with Iraq and Saudi Arabia.
The United States is concerned that Iran, a Shi'ite regional power, will take advantage of gains against IS in Iraq and Syria to expand the influence it gained after the US invasion in 2003, something Sunni Arab rivals such as Riyadh also oppose.
"Iranian militias that are in Iraq, now that the fight against Daesh and ISIS is coming to a close, those militias need to go home. The foreign fighters in Iraq need to go home and allow the Iraqi people to regain control," Tillerson said at a joint news conference with Saudi foreign minister Adel Jubeir on Sunday.
Tens of thousands of Iraqis heeded a call to arms in 2014 after IS seized a third of the country's territory, forming the Popular Mobilisation Forces (PMF), which receive funding and training from Tehran and have been declared part of the Iraqi security apparatus.
A senior US official said Tillerson had been referring to the PMF and the Quds Force, the foreign paramilitary and espionage arm of the powerful Islamic Revolutionary Guards Corps (IRGC).
Iraq's military, armed by the United States but supported by the PMF, ejected the ultra-hardline Sunni Muslim militant group from Mosul and other cities in northern Iraq this year.
The campaign to uproot the militants left whole cities in ruins and has hit Iraq's economy.
A new joint ministerial-level body between Iraq and Saudi Arabia convened its inaugural meeting earlier on Sunday to coordinate their fight against IS and on rebuilding Iraqi territory wrested from the group.
Jubeir emphasised historic ties between the two neighbours, which share a border, vast oil resources and many of the same tribes.
The rare senior meeting, signalling a thaw between states that have been at loggerheads for decades, was also attended by Saudi King Salman and Iraqi Prime Minister Haider al-Abadi.
