Combined Joint Task Force Operation Inherent Resolve, the US-led coalition fighting IS in Iraq is mostly made up of Iraqi and Kurdish Peshmerga fighters.
In a statement on Monday, commander of the anti-Daesh coalition Lt. Gen. Stephen Townsend, openly acknowledged the presence of "forward air controllers" amongst the US "advisory" contributions to the battle, The Guardian reported.
The controllers -- known as Joint Terminal Air Controllers (JTACS) -- are troops drawn from special operations forces to ensure greater accuracy of aerial bombardment.
Their presence indicates that US troops, while not formally in a combat role, are on the frontlines and are willing to use substantial airpower on Iraq's second city.
The US command's acknowledgment of their presence is the latest departure from US President Barack Obama's promise against having "boots on the ground" in Iraq.
"Americans are again playing an adviser role, an enabler role for these Iraqi forces," ABC news quoted Pentagon spokesman Peter Cook as saying at a briefing.
"Most of the American forces in Iraq are not anywhere close to the front line," he added.
The Iraqi operation to recapture the city of Mosul, the last stronghold of the Islamic State (IS) terror group in the war-torn country, began on October 17 with more than 54,000 Iraqi troops.
Mosul, nearly 400 km north of the Iraqi capital of Baghdad, has been under IS control since June 2014, when Iraqi government forces abandoned their weapons and fled, enabling the IS militants to take control of parts of the country's northern and western regions.