The Pentagon has accused the Islamic State (IS) extremist group of using thousands of residents of Mosul as "human shields" to try to thwart the advance of Iraqi forces into the city.
"We know they are being used as human shields, absolutely," Pentagon spokesman Captain Jeff Davis told reporters on October 18.
"This has been going on for several weeks where we've seen civilians being forcibly detained and their movements being prevented where they can't get out of Mosul. They are being held there against their will," he said.
Around 1.5 million people still live in Mosul and the International Organization for Migration said earlier on October 18 that IS may use tens of thousands of residents as human shields to hold onto their last city stronghold in Iraq.
The group also said there was a likelihood of chemical attacks by the extremists, who have used such weapons previously against Iraqi Kurdish forces.
The Reuters news agency reported that the Pentagon is expecting IS to use crude chemical weapons as it tries to repel government forces, and U.S. troops have begun testing IS shell fragments for evidence of chemical agents.
Davis said the operation to retake Mosul will be "an ugly fight."