The United States has publicly backed Iraq's prime minister in his confrontation with armed factions operating outside state control, with Washington's envoy to Baghdad saying militia influence has no place in the country's institutions.

Tom Barrack, the US special envoy to Iraq and Syria, said on Sunday that Prime Minister Ali Al-Zaidi was sending a clear message about who governs Iraq. "Militia influence has no place in Iraq's institutions," Barrack said, adding that Iraq's future belongs to its people rather than to armed factions operating outside the state. He described the prime minister's position as "sovereignty in action".

Barrack's remarks came hours after Al-Zaidi warned that his government would confront weapons held outside state control that threaten security or intimidate citizens, "through the full force of the law". The warning was the latest escalation in a standoff between the prime minister and Iran-aligned armed groups, above all Kataib Hezbollah, one of Iraq's most powerful factions.

The dispute has sharpened in recent days over the government's effort to bring faction weapons under state authority. Al-Zaidi has set out a plan under which armed groups are expected to place their arsenals under state control, with the process due to conclude by the end of June 2027. Washington has tied its support for his government to visible progress on that timetable, and President Donald Trump is reported to have warned Al-Zaidi by telephone that the United States would strike factions and their leaders if they joined any renewed war in support of Iran.

At the centre of the latest row is Mosul International Airport. Al-Zaidi ordered the cancellation of three service contracts at the airport, covering check-in counters, a car park and a taxi office, after they were linked to armed groups. The contracts are to be reassigned to international companies instead. The airport, which reopened after extensive reconstruction following the war against the Islamic State group, has become a symbol of the wider struggle over who controls state facilities and the revenue they generate.

Kataib Hezbollah has denied controlling the airport contracts and has pushed back hard against the prime minister's campaign. The faction urged Iraq's Integrity Commission to investigate the finances of Hassan Al-Zaidi, the prime minister's brother, and alleged that intermediaries handling donations to armed groups still owed five million dollars. The exchanges underline how personal and political the confrontation has become.

Behind the scenes, senior Shia figures have moved to prevent the standoff turning into armed confrontation. Ammar al-Hakim, leader of the National Wisdom Movement, and Humam Hamoudi, leader of the Islamic Supreme Council, have begun mediating between the two sides with the backing of parties within the Shia Coordination Framework, the alliance that nominated Al-Zaidi and dominates the government.

The mediation faces a difficult task. Most of Iraq's Iran-aligned factions run brigades inside the Popular Mobilization Forces, a state-funded umbrella formed in 2014 to fight the Islamic State group, while keeping their own chains of command. Their political wings and allies are estimated to hold roughly 60 to 70 of parliament's 329 seats. Two of the groups furthest from any understanding with the government, Kataib Hezbollah and Harakat al-Nujaba, are also the ones most closely bound to Tehran.

Barrack's intervention signals that Washington is firmly behind Al-Zaidi's push for state authority, at a moment when the risk of a renewed United States-Iran war hangs over the region. Whether the prime minister can convert that backing into control over the factions' weapons, without triggering the confrontation his mediators are trying to avoid, remains the open question in Baghdad.