On the roof of a house in northern Syria, a foreign soldier from the US-led coalition against the Islamic State group monitors progress towards the jihadist bastion of Raqa.
He is one of a few dozen advisers from the international coalition helping a Kurdish-Arab alliance known as the Syrian Democratic Forces advance towards IS group's Syrian stronghold.
The advisers are leery of journalists, demanding that an AFP photographer stop taking photographs and leave when they spot him.
SDF sources say that around 50 foreign troops are involved in the operation, which began on November 6, primarily to guide anti-IS coalition air strikes.
AFP journalists on the ground have seen soldiers with US markings on their uniforms, along with others speaking French.
The coalition's press office declined to detail the number of its forces on the ground, or their nationalities, but confirmed they were playing a wide-ranging role in the fight for Raqa.
"As part of the coalition's commitment to advise, assist and accompany the SDF, we are asked to help with operational planning, the coordination of air strikes, arranging troop movements, training and supplying equipment to the SDF for the isolation of Raqa," a spokesperson told AFP.
In the village of Al-Huriya, one adviser peers through binoculars at the fighting in the nearby village of Al-Heisha, which SDF fighters eventually wrenched from IS control on Friday.
On radios, SDF fighters can be heard relaying details to commanders about their progress and where they might need help from the coalition aircraft flying constantly overhead.
"The forces advancing on the ground give us coordinates close to the targets," says SDF commander Ahmed Osman, in the yard of another house that has been turned into a command centre.
"They calculate the distances between them and the mercenaries and work out where the fire is coming from, then they send us the coordinates and we transmit them to the coalition so the targets are hit."
The strikes are sometimes used against one of IS group's favoured weapons: suicide car bombs.
"Sometimes we take them out with our weapons, but other times coalition aircraft strike them after we tell them the coordinates," Osman says.
The US-led coalition began strikes in Syria in September 2014, and has worked closely with Syrian Kurdish-led forces to push IS group from large swathes of territory.
Such cooperation has angered Washington's NATO ally Turkey, which considers the main Syrian Kurdish YPG militia a "terrorist" group, and is currently waging its own offensive inside Syria, targeting both IS and the Kurds.
On the ground, SDF vehicles speed through the desert towards the front line, despite the mortar rounds IS fires as it struggles to hang on to Al-Heisha.
"Our comrades are preparing for an attack, and the mercenaries are firing mortars, but planes are over the region now," says Akid Kobane, another SDF commander.
Kobane says the air strikes are a key part of the SDF assault, considered a precise way to target IS while minimising civilian casualties.
"IS is using civilians as human shields," he says.
"We're not using heavy weapons in the battle for Raqa, we're relying on personal weapons and the coalition's strikes."
In a bid to protect themselves, some civilians have raised white flags on their roofs, but there have been allegations of civilian deaths in air strikes.
The Syrian Observatory for Human Rights, a Britain-based monitor, reported at least 20 civilians killed in coalition strikes on Al-Heisha on November 9.
An SDF spokeswoman at the time dismissed the report as IS propaganda, although the coalition said it was investigating the incident.
Civilians who have fled the fighting confirm that IS is embedded among local residents.
"There are always strikes on areas where Daesh (IS) is present... and Daesh hides itself, even among children," says 38-year-old Amsha at a makeshift camp for displaced civilians outside the town of Ain Issa, around 50 kilometres (30 miles) north of Raqa.
"Our children are terrified when the planes are overhead. We've a little girl who shrieks 'Plane, plane!' each time she hears one and runs to hide," she says.
"Daesh would hide explosive-packed cars between houses to try to conceal them from the planes," adds Ghada, in her twenties.
"The jihadists would tell us they had no problem dying, so why would they care if civilians are killed alongside them?"