U.S. troops in Iraq are setting up a train-advise-and-assist team at a forward operating base near the Islamic State group's front lines outside of Mosul, not far from the site of recent chemical weapons attacks.

The Nineveh Operations Center in the farming village of Makhmour will be a primary base for the U.S. to support the Iraqis' long-awaited battle to seize Mosul from Islamic State militants, also known as ISIS or ISIL, a U.S. military official said.

A large convoy of Iraqi army forces began arriving at the base in Makhmour in early February. Iraq's military leaders plan to deploy about 4,500 soldiers to the area for the Mosul operation, Iraqi officials said.

"There's a lot going on in Makhmour. That's where one of our operations centers is located. So there are American advise-and-assist capabilities there," said Army Col. Steve Warren, a U.S. Defense Department spokesman in Baghdad.

Makhmour is along the edge of the Kurdish-controlled territory near the ISIS-held Tigris River valley and is near the site of a mustard gas attack last year and also a foiled ISIS attempt to launch chlorine gas rounds. A new mustard gas attack was reported in the area Wednesday.

Makhmour now has U.S. advisers as well as a team of U.S. troops providing force protection, Warren said. It's also a new headquarters and command center for the Iraqi army's 15th Division, a unit that participated in an American-led training program last year.

"That's going to become an area that really kind of directs, I think, the battle going forward" toward Mosul, Warren said.

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"They will begin the process of generating the combat power that's necessary to ... progress this campaign with an eventual goal of Mosul."

Warren declined to say how many U.S. troops are in Makhmour. There are about 3,700 American forces deployed throughout Iraq.

Last August, ISIS fired shells filled with chemical weapons that landed near Makhmour and sickened dozens of Kurdish troops. U.S. military officials later confirmed that the shards of spent mortar shells tested positive for mustard gas, also known as "HD."

A defense official familiar with the attack said on Wednesday that the mustard-laden shells were not "danger close" to the operations center with U.S. troops.

In November, Kurdish officials said ISIS set up a mortar battery loaded with shells filled with chlorine gas about 15 miles south of Makhmour. The Kurdish peshmerga found and diffused the mortars before they were launched, Kurdish officials said in November.

On Wednesday, Kurdish officials reported a new chemical weapons attack near Makhmour. Three peshmerga fighters were wounded by Islamic State shells loaded with mustard gas, according to a Rudaw Kurdish media network report.

The Army considers the threat of chemical weapons in its force protection planning for U.S. troops in the region, said Army Lt. Col. Cathy Wilkinson, a Defense Department spokeswoman in Baghdad.

"Coalition force protection is a top priority," Wilkinson said in an email Thursday.

"Predeployment training prepares service members to properly react to chemical, biological, and radiological events. We take the risk of Chemical Weapons use into consideration as part of our force protection measures and are prepared to respond to such a contingency.

"The use of chemical weapons reinforces why the international coalition is assisting the Iraqi government to degrade and ultimately destroy ISIL, which continues to kill indiscriminately and is completely unencumbered by any legal or moral restraint.

"The coalition has provided more than 10,000 protective chemical masks to the Iraqi Security forces and Peshmerga," she said.