A detachment of US Marines has been dispatched to Iraq to join the ground fight against Isis.

The Marines sent are from the 26th Marine Expeditionary Unit (MEU), an air-ground fighting force of 2,200 soldiers. However, it is not clear how many of these soldiers will actually be deployed to Iraq.

There are around 3,600 US army personnel already stationed in Iraq. They are leading air strikes against Isis forces, supplying arms to the Kurdish peshmerga, carrying out humanitarian air drops and providing intelligence and support to the Kurdish and Iraqi armies.

Inside Isis secret tunnels Show all 7 1 /7 Inside Isis secret tunnels Inside Isis secret tunnels Network of underground tunnels was discovered by Kurdish forces after they regained the town of Sinjar in Iraq Inside Isis secret tunnels A member of the Peshmerga forces inspects a tunnel used by Isis militants in the town of Sinjar, Iraq Reuters Inside Isis secret tunnels An entrance to the tunnel used by Islamic State militants is seen in the town of Sinjar, Iraq Inside Isis secret tunnels The secret tunnels allowed militants to freely move underground Inside Isis secret tunnels The tunnels appear to be wired with electricity Inside Isis secret tunnels Some of the tunnels are 30 feet deep Inside Isis secret tunnels Concerns remain that parts of the tunnels are rigged with explosives

There have been occasional ground clashes between Isis fighters and members of the US-led coalition, but the primary role of the US has been in supporting Iraqi and Kurdish ground troops with air strikes as they attempt to retake Isis-controlled territory.

US special forces have made occasional forays into Isis territory, for example liberating 70 hostages during a raid in October 2015. A US sergeant was killed in the assault.

The news comes one day after an American Marine was killed in a rocket attack. It was the second combat death of a US serviceman in the country since the US-led intervention against Isis began.

Though the role of the Marines is yet to be revealed, the latest deployment is a significant step towards the use of conventional warfare tactics. Such a shift in policy is a politically divisive move in the US in the aftermath of the protracted and bloody Iraq war.

Speaking in January, US Defense Secretary Ash Carter said: "We're looking for opportunities to do more, and there will be boots on the ground. I want to be clear about that."

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His comments were echoed in February by the top-ranking US general in Iraq.

Lieutenant General Sean MacFarland said: "We have shifted from a pure counterinsurgency focus and are now preparing the [Iraqi security forces] to conduct what we refer to as combined arms operations,

"There is a good potential that we will need additional forces to provide those capabilities. The ability to integrate infantry, armor, artillery, air power, engineers and other assets on the battlefield provides the Iraqis with a decisive advantage over a static enemy dug in behind complex obstacle belts."

A 2015 poll revealed that a slight majority of US citizens were in favour of boots-on-the-ground intervention, with 53 per cent of respondents backing the move.