Lying in wait: Rigged toys and teddy

Isis fighters fleeing their self-declared capital in Raqqa, Syria, have left behind an unprecedented array of deadly improvised explosive devices, US officials say, forecasting whats expected to be a years-long effort to purge them.

Only about 100 militants remain in the city, but the sophisticated explosives theyve rigged are slowing efforts to declare a full victory there and could pose grave challenges for Raqqas residents as they begin to rebuild after the months-long battle to expel the Islamic State.

The fight in Raqqa is as much about the fight against IEDs as a fight against Isis, Army Colonel Ryan Dillon, a spokesman for the US-led coalition in Syria and Iraq, said.

He echoed remarks made recently by a commander with the Syrian Democratic Forces, the principal group opposing Isis there.

The weapons range from hastily rigged bombs to hidden pressure plates and motion-activated explosives.

They have been found under floors, concealed in ovens and drawers, and attached to corpses and childrens toys. In at least one instance, a teddy bear was rigged to explode.

The threat lurks with every step made by troops fighting to liberate the city and the Raqqa Internal Security Force, a local policing unit of about 1600 that will try to keep the peace there once the offensive ends. Its commander, Idris Khan, was killed by an IED strike on Tuesday.

Two SDF soldiers also died in the blast. The use of IEDs and explosives is more dense than other cities weve seen in this campaign, Dillon said, including the Iraqi cities of Mosul, Ramadi and Fallujah.

All those cities were heavily mined by Isis fighters looking to kill coalition troops sweeping through them to reassert government control.

Surpassing the scope of rigged munitions in Mosul would be significant. Following its liberation, United Nations and US State Department assessments concluded that it could take more than a decade to remove the remaining explosives. It is unclear when such assessments will be made for Raqqa.

The UN estimated that 300,000 people have fled Raqqa since before the offensive there began in April. Between 10,000 and 25,000 remained as of August.

Soon, the State Department will lead five multiagency teams into Raqqa, where theyll help identify and clear munitions and provide humanitarian assistance, an official there said. As part of that, officials will educate returning residents about the weapons hazards.

They face a problem three years in the making. Bomb builders have circulated lessons and best practices from Iraq and Afghanistan during the reign of Isis in Raqqa, creating a de facto laboratory for experts to hone their craft.

That expertise will also challenge members of Raqqas police force, who receive 10 to 15 days of general training which includes basic counter-IED instruction, Dillon said. It does not include how to defuse and remove the weapons.

Some receive additional training focused on such skills, he added, but he was unsure whether the Pentagon is providing any specialised safety equipment such as bomb suits or robots.

The lack of experience among the forces concerns Matthew Hefti, a former Air Force bomb technician with two deployments each to Afghanistan and Iraq.

Bombers often target what troops call fatal funnels - confined places such as hallways, stairwells and doorways. So those tasked with clearing bombs will need to study those places to identify where the militants may have safely ventured.

You have to be unpredictable. You have to do the opposite of what the bomber thinks youll do.