The cars slowed as they approached a berm on the northern outskirts of this small town. A Kurdish peshmerga fighter at the checkpoint, instead of waving them through, began pointing urgently to the left — just as the whistle-boom of a mortar shell, a close one, sounded nearby.
Soon there was more trouble: Humvees and armored vehicles careened in and quickly set up defensive positions behind the berm. Several civilian cars were right behind, their terrified drivers gunning their engines to escape the crescendo of explosions they had just left behind.
The bangs now came from all sides, intensifying into a drum roll as the peshmerga's heavy machine guns opened fire at advancing Iraqi forces, accompanied by the bass thumps of the Howitzer artillery at the rear. The high-pitched whines of bullets whizzed past, one smacking into a vegetable stall, another piercing the trunk of a car.
The clashes Friday between Kurdish forces and Iraqi troops — until now allies in the fight to dislodge Islamic State from Iraq — marked the heaviest round of violence since Baghdad launched an offensive earlier this week to claw back disputed areas also claimed by the semiautonomous Kurdish region in northern Iraq.
Elite Iraqi special forces, federal police and Iranian-backed paramilitary units known as Hashd al Shaabi engaged Kurdish troops, advancing from Kirkuk to Altun Kupri district, 25 miles northwest and almost halfway to Irbil, the capital of the Kurdistan regional government.
Throughout Friday's conflict, a drone piloted by the U.S.-led coalition patrolled the skies above, but did not attack any of the belligerents.
"America and Kurds are friends. Why aren't they bombing Hashd and Iran?" asked one peshmerga fighter, whose angry protest was momentarily interrupted by the whistle of an incoming mortar.
The outcome appeared to be a standoff: The Iraqi army announced that its forces had "imposed security" in the district; a statement released by the general command of the peshmerga said the Iraqi attack had been "defeated."
The taking of Altun Kupri, a Turkmen-dominated town on the Zab River that separates Kirkuk from Irbil, is the latest in a series of crushing setbacks for the Kurdish government, which in the last week has lost some 40% of the territory it hoped to include in a future Kurdish state, as well as half of its projected oil reserves.
It is also a troubling development for the U.S.-led coalition, which has lavished both the peshmerga and Iraqi forces with weapons and logistical and air support in the fight against Islamic State. Some of those weapons and vehicles were seen on the front line during Friday's skirmish.
Kamal Karkouki, commander of the peshmerga in western Kirkuk, said in an interview, "Iraq attacked the area here with American weapons, and we have to answer them."
"They will try to occupy this whole area and move forward," he said.
Spokesman Col. Ryan Dillon said the coalition was "aware of the incident" and that it was continuing "to engage our counterparts in the Iraqi army and the peshmerga to ease tensions … there is also work on the embassy level as well."
The U.S., which opposed a nonbinding referendum last month on Kurdish independence, has insisted it will not take sides. But Dillon said that both peshmerga and Iraqi army leaders, while diverted over the independence debate, were "not as responsive or committed to the fight against ISIS … and this has always been our concern leading up to the referendum, and it has certainly played out in that way and more so right now."
Islamic State is also known as ISIS.
"Just because ISIS doesn't hold territory doesn't mean they're not planning attacks or planning nefarious activity all over Iraq, and this is something we have to keep an eye on," said Dillon. "We're already seeing the emphasis and the attention on ISIS slipping away."
Casualty numbers were not immediately disclosed, but witnesses said at least eight peshmerga had been treated for wounds.
Karkouki later said that his fighters had destroyed five Iraqi Humvees and two tanks, while a reporter in the area saw two peshmerga vehicles burning after apparently taking direct hits from mortar fire, as well as the charred skeletons of three pickup trucks.
The clashes come after a relatively bloodless offensive forced peshmerga units in the past week to hand over oilfields, power plants, airports as well as important border districts to Iraqi forces, almost without a shot being fired. Baghdad is seeking to reimpose its control over areas the peshmerga had seized after Islamic State's stunning 2014 takeover of northern Iraq.
But Friday's fighting also signified a further souring of already-tense relations between the Kurds and the Iraq government more than three weeks after the overwhelming Kurdish vote in favor of secession.
Kurdish news outlets have been full of reports of Kurdish neighborhoods facing harassment by Iranian-backed Shiite militias allied with the central government (the reports were dismissed as "fake news" by Iraqi Prime Minister Haider Abadi).
The U.S. State Department said it was "concerned" by the clashes and appealed for all parties "to cease all violence and provocative movements, and to coordinate their activities to restore calm."
The department statement said the Iraqi government's reassertion of authority over disputed areas in the north "in no way changes their status— they remain disputed until their status is resolved in accordance with the Iraqi constitution."
Meanwhile, in his Friday address, Grand Ayatollah Ali Sistani, Iraq's top Shiite cleric, called on Baghdad to do more to reassure and protect Kurdish citizens.
He also advised Kurdish leaders to "unify their ranks and work to get past the current crisis through cooperation with the central government," in accordance with the constitution.
5:40 p.m.: This article was updated with a statement from the U.S. State Department.
2:50 p.m.: This article was updated throughout with staff reporting.
7:50 a.m.: This article was updated with additional details.