The US-led coalition against Islamic State has begun surveillance flights over the Iraqi city of Tikrit, which is being besieged by government forces.
Coalition officials said the support was requested by the authorities in Baghdad. They would not say whether air strikes would also be carried out.
Until now, the US had no involvement in the Iranian-backed operation in Tikrit.
But a Pentagon spokesman said the assault had “stalled”, with IS militants in the city centre “dug in”.
This is the first attempt to push out IS from a major urban centre in Iraq and is seen as a test for an operation to retake the country’s second largest city, Mosul, which along with Tikrit was seized last June.
‘Eye in the sky’
The operation to retake Tikrit, which lies about 160km (100 miles) north of Baghdad, began earlier this month with more than 20,000 soldiers, police and Shia militiamen from the Popular Mobilisation (Hashid Shaabi) units attacking from all directions.
Iranian military advisers – led by Gen Qasem Soleimani, commander of the Revolutionary Guards’ Quds Force – helped co-ordinate the assault.
Despite having no support from coalition aircraft, the government’s forces made rapid advances, capturing outlying towns and villages along the River Tigris and entering northern and southern districts of the city.
But the offensive has since stalled in the past two weeks, with the army and militia suffering heavy casualties and the city centre remaining firmly in the control of several hundred IS militants, who have planted a large number of bombs in roads and buildings.
“Frankly [the operation] has not gone forward recently,” Pentagon spokesman Col Steve Warren told reporters in Washington on Tuesday.
Col Warren said Iraqi troops had encircled Tikrit, but had only made “minor inroads” on the city’s outskirts.
“The enemy is dug in there,” he added, with “fairly hardened and sophisticated defences”.
Col Warren would not confirm that the Iraqi government had requested any assistance from the US, but said that if it did, “we would take a look”.
Earlier, a senior coalition military official told the AFP news agency the US had begun providing intelligence, surveillance and reconnaissance (ISR) support on Saturday at the request of the Iraqi government. The support took the form of “an eye in the sky”, the official added.
Coalition officials declined to discuss whether the US was or would be also carrying out air strikes in support of the Tikrit operation, or directly communicating with Iranians on the ground.
The need for coalition air support has been a point of contention between the Iraqi military and the Popular Mobilisation, which had opposed it.
Hadi al-Amiri, the head of the powerful Iranian-backed Badr Brigade militia, told journalists on Sunday: “Some of the weaklings in the army… say we need the Americans, while we say we do not need the Americans.”
- The Popular Mobilisation (Hashid Shaabi), comprising dozens of Shia militias, takes a lead role in Iraqi operations against IS. Its fighters have also been accused of committing atrocities and acting with impunity
- It was formed by the Shia-led Iraqi government in June 2014 after the army collapsed in the face of an advance by IS across northern Iraq
- Iran provides funding, weapons and military advisers to the Popular Mobilisation militias and reportedly controls several of them directly
- The Popular Mobilisation is headed by Jamal Jaafar Mohammed, also known as Abu Mahdi al-Mohandis, a former Badr Organisation commander who is close to Iranian General Qasem Soleimani