Iraqi forces have begun an operation to retake the western half of Mosul from the Islamic State terror group, reportedly supported by SAS and SBS soldiers.
Western special forces have been deployed to help deal with car bombs in parts of the city already taken, according to the Times newspaper.
Prime Minister Haider al-Abadi announced the start of the operation early on Sunday morning on state television.
He said government forces were moving to "liberate the people of Mosul from Daesh oppression forever", using the Arabic acronym for IS.
South-west of Mosul, near the city's IS-held airport, plumes of smoke were seen rising into the sky as coalition aircraft bombed militant positions.
Further south at an Iraqi base, police forces were gathering and getting ready to move north.
Iraqi forces took control of eastern Mosul last month, but the west remains in the hands of entrenched extremists.
Mosul, Iraq's second-largest city, is roughly split in half by the Tigris River.
The battle for Mosul's western half is expected to be prolonged and difficult, due to the older, narrower streets.
30 SAS and SBS soldiers are said to be embedded with Iraqi and Kurdish forces, along with 450 American special forces.
In fact, Canadian and French special forces have also been deployed in training and advising roles.
However, the special forces' advisory role could change if required in an emergency, claims the Times:
"The SAS in Iraq... are embedded with the Iraqi and Kurdish security forces and if their assistance is urgently required there is no question that they will leap forward, all guns blazing, to protect the men they have trained."
Unable to discuss special forces, no MP can respond to the claim that Special Forces are, or could end up being, 'advisers' in name only.
The situation is a little different in the US because the Pentagon has had to acknowledge that the combat deaths of some US special operations personnel must have resulted from combat.
Under US law, Title 10 and Title 50 give guidelines that allow for more secrecy in the case of the latter (CIA operations, usually, that often require special forces backup), and for the acknowledgement of the presence of special forces soldiers in a given theatre in the case of the former.
Cover image: A member of the Kurdish Peshmerga