TWISTED ISIS killers have been rigging mass graves of slaughtered innocents with booby trap bombs, The Sun can reveal.

Terror state killers have wired multiple graves of up to 4,000 dead men, women and children with devices in a bid to kill heart-broken relatives desperate to retrieve remains for proper burial.

The gruesome tactic – now being uncovered across liberated ISIS territory – is being dealt with by UN de-mining forces funded by vital Dfid aid.

Former British soldier David Parker, 44, a married dad of two, from Kent, is working with the UN Mine Action Service mission currently ridding war ravaged Iraq of thousands of buried bombs.

He told The Sun fleeing ISIS killers had left devices “literally everywhere” including mass graves left after death state henchmen massacred entire thousands.

He said: “Recently, we pushed toward Tal Afar to help clear it.

“We had a meeting with the mayor and he turned around to us and explained there was a natural sink hole a couple of kilometres out and ISIS had massacred 4,000 people, and basically put them in a sink hole.

“Then what they did was booby trapped the bodies and booby trapped all the access to it - laid IEDs all around this sink hole - so people couldn’t reclaim the bodies.

“That’s the most shocking thing I’ve come across. The mayor at Sinjar knows of at least seven mass graves in his region that require clearance.

“As we clear areas we are going to find more mass graves.”

Experts estimate “tens of thousands of explosives” have been left by Daesh to kill over two million innocents trying to return home after years of war.

This year alone over 15,000 explosives have been made safe in Iraq, as well as 750 suicide belts and 330 deadly traps – some found in schools, hospitals and kids’ playgrounds.

Britain is one of the biggest financial donors to the work – with the Department for International Development and the Conflict Stability and Security Fund giving £14.2m since 2015.

Thanks to that money in the last two years 663 sites being cleared of explosive hazards, and 4.4million square metres of land made safe.

Last year Dfid committed to triple global spending on mine action to £100m over two years.

So far the UK-funded work has discovered a hospital used as a Daesh HQ in Mosul where 3,500 explosives had to be secured.

Another hospital had been rigged to blow – even though it was the main maternity and children’s hospital for 500,000 people.

A school in Fallujah was found to be rigged with 13 IEDs – which could have killed any of the 250 boys and 200 girls who attended the school.

Another school in Mosul was found with 15 suicide belts.

Former Warrant Officer David, who runs contractor teams to clear sites, praised Dfid’s role in the mission, saying: “People are still dying from what was left behind from the war and we have hardly scratched the surface.

“I think the British people should be really proud about what we’re achieving here.”