British SAS troops injured fighting Isis near Mosul in Iraq

These are thought to be the first combat related casualties of Britain's renewed involvement in Iraq

A British special forces commando in training (Jeff J Mitchell/Getty Images)

Three British special forces operatives have been injured in a firefight with Isis militants in Iraq.

The engagement took place during a covert reconnaissance operation near Isis-held Mosul, in the north of the country.

The soldiers, believed to be from the Special Air Service (SAS) and Special Boat Service (SBS) regiments, suffered bullet and fragmentation injuries, the Mirror said.

They are the first reported combat casualties of Britain's involvement in Iraq against Isis, known as Operation Shader.

While the Government does not comment on special forces operations, it is believed that the soldiers were part of a mission with German and American soldiers.

"The enemy were up to 30 strong and heavily armed," a 'highly placed source' told the Mirror. "An air strike was needed to resolve it."

The source also alleged that there was a "secret" war being waged against Isis.

Government ministers would "hide behind the claim they can’t comment on special forces operations to avoid acknowledging Britain is at war," he told the Mirror.

"Publicly to acknowledge these heroic men were injured would be to admit the battle took place and they cannot do that because it is all being done off the radar."

“Politically no one has an appetite for open war against Isis so it’s done in secret.”

The UK's combat engagement as part of Operation Shader so far has been from the air. The RAF have flown over 340 missions, targeting Isis fighters, bases, combat vehicles, ammunition dumps, and communications and training facilities.

In December 2015 the number of British troops in Iraq was just 275 and The Independent reported that a visiting Common's defence committee complained about the small number of British troops and how far they were from the frontline.