The attack started at dawn in Fallujah's Nuaimiya area where Iraqi troops captured almost 85 percent of the ground the previous day, two officers with the Special Forces told The Associated Press.

ISIS (ISIL, IS) militants used tunnels, deployed snipers and sent six explosives-laden cars to hit the troops but they were destroyed before reaching their targets, the officers said, speaking on condition of anonymity.

Tunnels — similar to those found in other territory long held by ISIS — have already been discovered in the northeastern outskirts of Fallujah.

Nuaimiya is a sprawling mainly agricultural area in Fallujah's south and Monday's push into it was the first attempt by Iraqi forces to enter the city after focusing on dislodging the militants from surrounding areas to tighten the siege.

The Iraqi counterterrorism forces are leading the assault on Fallujah, slowly moving up from the southern edge. Their advance is expected to be slow also because tens of thousands of civilians remain trapped in Fallujah and hidden bombs are believed to be strewn throughout the city, according to Special Forces' commanders at the scene.

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