Iraq's ruling alliance and powerful Shiite militias say Prime Minister Haider al-Abadi would be digging his own political grave and undermining the fight against Islamic State if he permits the deployment of a new US special operations force in the country.
Washington said on Tuesday it would send troops, expected to number around 200, to Iraq to conduct raids against the ultra-hardline Sunni Muslim militants who have seized swathes of the country's north and west, and neighboring Syria.
Abadi said hours later that any such deployment would require his government's consent, comments that may have been made for public consumption at home.
US Secretary of State John Kerry maintained on Wednesday that the Iraqi government had been fully briefed on the plans and said the two governments would consult closely on operational details.
But Abadi's political partners said they would never accept an expanded role for US troops and insisted the premier would not dare act alone after parliament withdrew support for his domestic reform agenda last month over concerns he did not consult widely enough before making important decisions.
"If Abadi makes a unilateral decision to approve the deployment of American special forces, we will question him in parliament. He is aware that a questioning could lead to a vote of no confidence," said Mohammed Naji, a lawmaker from the Badr Organisation and a local leader in the Hashid Shaabi, which groups Shiiite militia and other fighters against Islamic State.
Abadi faced a major challenge in November from within his own Shiite ruling coalition when parliament voted unanimously to bar the government from passing important reforms without its approval.
The move, seen as an effort to curb Abadi amid discontent over his leadership style and the slow pace of reforms demanded by protesters, stirred speculation about an attempt to topple him but such fears have lately subsided.
"The government is not allowed to authorize a deployment of American troops in Iraq even if they are expeditionary or intelligence gathering forces," said Hakim al-Zamili, a leading Shiite politician from the Sadrists, a movement founded by anti-American cleric Moqtada al-Sadr.
Ammar Tuma, leader of the Fadhila party in the Shiite alliance, backed that position, arguing that only parliament, not Abadi, has the authority to approve the presence of foreign combat forces.
Resistance to any expansion of the US role in the country, no matter how limited or gradual, stems in part from absolute mistrust among Iraqis and their leaders of Washington's intentions.
Naji said he feared that once deployed, US special forces might eventually turn their attention to pursuing Hashid Shaabi commanders and key Shiite politicians, some of whom are on the US terrorism watch list.
"For Abadi to give a green light for the American troops to deploy in Iraq would not be a shot in the foot," said another lawmaker from the Shiite alliance. "It would be a shot in the head."
Opposition from Shiite militias, seen as a bulwark against the Islamic State insurgents posing the biggest security threat to major OPEC oil exporter Iraq since the fall of Saddam Hussein in 2003, could also force Abadi to stall Washington's plans.
The prime minister has been under mounting US pressure to rein in the Iranian-backed armed groups, angering the forces who enjoy support from many of Iraq's majority Shiites.
Lawmakers said Abadi would not risk a confrontation with the paramilitaries, but it will be difficult for him to resist pressure from Washington, a major donor to the Iraqi military, to give US troops a wider combat role.
"It's nearly an impossible mission for Abadi to find a compromise. He has to make sure not to provoke his coalition and powerful Shiite Hashid groups and at the same time respond to the Americans," said Baghdad political analyst Ahmed Younis.
"If Abadi accepts the deployment of American special troops, he offers his rivals on a silver platter the chance to sack him."
Militia leaders have already rejected any deployment of US forces and said they would not hesitate to turn their attention from battling Islamic State in order to fight the Americans.
Shiite militias put up fierce resistance to the US occupation that followed Saddam Hussein's overthrow.
Jafaar Hussaini, a spokesman for Kataib Hezbollah, one of the main Iranian-backed Shiite militant groups, said sending US forces would only worsen the security crisis in Iraq.
"Anybody, including Prime Minister Abadi, who approves the presence of American troops in Iraq should bear responsibility for triggering an all-out civil war," he said.
While such warnings may be premature, an increase in direct US military activities -- even on a small scale -- could fuel instability and undermine chances of containing the sectarian conflict.
The last US troops withdrew in 2011 but some returned as advisers in 2014 after Islamic State's advance threatened Baghdad and they now number around 3,500.
Russia's larger military role in Syria and its participation in a security coordination cell in Baghdad that includes Iran and Syria has raised concerns in Washington that it is losing ground to its former Cold War foe in the Middle East.
Naji, the Badr lawmaker, said deploying US troops to Iraq would be "a magnet" that would attract more meddling by foreign powers.
"We will be a courtyard for other powers to settle their own scores," he said.
