The offensive to retake Mosul is advancing as troops close in on territories captured by Islamic State terrorists.
Last week, more than 50 ISIS fighters stormed government and security compounds around the northern Iraqi city of Kirkuk, about 100 miles from the frontlines of the Mosul offensive, killing at least 80 people.
Jihadists launched another attack this past weekend on the town of Rutba in western Iraq, hundreds of miles from Mosul.
"What happened in Kirkuk might be an introduction to a series of operations, and we cannot rule out the targeting of Baghdad," Ahmed al-Sharifi, a Baghdad-based military analyst, said. "There are sleeper cells all over Iraq, particularly in Baghdad."
Some reports say ISIS may be using new, non-conventional weapons, including crude chemical weapons in Syria and Iraq.
Last month, an ISIS rocket armed with sulfur-mustard, a chemical agent that causes skin blistering, was used in an attack on a military base near Mosul housing hundreds of U.S. troops.
No one was wounded in the attack, but Marine Gen. Joseph Dunford, chairman of the Joint Chiefs of Staff, called it a "concerning development."
The Islamic State has also deployed more than a dozen explosives-laden armored vehicles against troops since the Mosul operation began.
"Every time we think we've countered terrorist tactics, something new always happens," said David M. Witty, a retired U.S. Army Special Forces colonel and former adviser to Iraqi Special Operations forces. "There's no end to it."