An SAS soldier decapitated an ISIS terrorist using only a spade after their unit was ambushed by militants during a patrol in eastern Afghanistan.

The veteran sergeant is said to have cut-off the gunman's head in one swoop after running out of ammunition during a fierce six-hour gun battle.

After killing him, the elite soldier then used the jihadist's own weapon to kill more ISIS henchmen.

An SAS soldier decapitated an ISIS terrorist using only a spade after their unit was ambushed by militants during a patrol in eastern Afghanistan (stock)

The deadly battle took place six weeks ago following a meeting between the SAS and former Taliban members now on the side of the Afghan government, the Daily Star reports.

When the special forces unit was ambushed by the ISIS gunmen, the Brits were forced to take refuge in a farm, picking off the attackers while under heavy fire.

But despite their skilled field combat the soldiers began to run low on bullets, leaving them sitting ducks.

The soldiers radioed their base calling for air support but could not tell whether the message was received.

Fearing that their time was up, the soldiers made a pact to fight until the death instead of being captured and tortured on camera before a public execution.

Some of the English speaking jihadists taunted the Brits warning they would send their decapitated heads back to their wives.

Our source said: 'The SAS thought they had seen their last day.

'They made a pact that they wouldn't be taken alive and vowed to fight to the death.

The sergeant - a veteran of dozens of battles - is said to have cut-off the gunman's head in one swoop after running out of ammunition during a fierce six-hour gun battle

'Capture would mean torture and a filmed execution and they weren't prepared to let that happen.

'They made every bullet count and when they ran low on ammo they waited for the jihadis to get close enough so they could be killed with grenades or using rifles as clubs – that was when one of the SAS managed to kill a man with a spade.'

Despite both gaining ground in Afghanistan of late, ISIS and the Taliban view themselves as enemies with differing ideological views and aims

But just as it seemed the brave SAS soldiers were going to be overwhelmed by the ISIS terrorists, two US Apache helicopter gunships appeared, forcing the insurgents to withdraw.

A US Chinook followed and rescued them.

By the time they arrived half the SAS unit had no ammunition left.

Despite both gaining ground in Afghanistan of late, ISIS and the Taliban view themselves as enemies with differing ideological views and aims.

Hundreds of fighters are believed to have moved in from Syria and Iraq fleeing the caliphate they declared in 2014.

Such is the threat the influx of new jihadists into the war-torn region, the UK is thought to be doubling its amount of SAS soldiers in Afghanistan in the next few weeks to around 100.