IS overran large areas north and west of Baghdad in 2014, but Iraqi forces have since regained significant ground, and Mosul is the last Iraqi city still held by the jihadists.
Iraq launched a massive operation to retake Mosul from the extremists a little more than two weeks ago, and its forces have reached the eastern outskirts of the city.
The United Nations has cited reports of IS kidnapping thousands of people for use as human shields, and also of the jihadists executing nearly 300 people in the Mosul area since October 25.
One resident of east Mosul said the IS jihadists had "demanded that people, especially young people, gather in the area's schools, and that they bring their identity papers with them".
But most people had "refused to obey those orders," Abu Yunes told AFP, adding they were fearful that IS wanted to use them as human shields
Abu Mohammed, a west Mosul resident, said IS had "gathered a large number of people from areas south of Mosul and forced them to move to the city."
He said that IS aims to hide among the civilians when security forces enter the city and flee among them to escape.
"The majority of Daesh members are now deployed on the right bank, and they are apparently ready to fight, after they prepared car bombs and suicide bombers and snipers, as well as rigging streets and bridges" with explosives, Abu Mohammed said, using an Arabic acronym for IS.
Mosul is split by the Tigris River, with the eastern half of the city known as the left bank and the western as the right bank.
Abu Mohammed's description of IS deployments squares with expectations the jihadists will put up the toughest fight in western Mosul, which is still not cut off from territory they hold farther west in Iraq and in Syria.
In Geneva on Tuesday, the United Nations said it had received reports of IS fighters forcing thousands of civilians into Mosul, possibly to be used as "human shields".
UN rights office spokeswoman Ravina Shamdasani told reporters there was "a pattern" of the jihadists surrounding their offices and bases in Mosul with civilians.
