However, there have been instances in which US troops have been killed or injured while operating under these strict guidelines.
US officials had said Wednesday that an oily substance found on a fragment of the rocket that landed inside the security perimeter of the base initially tested positive for mustard agent, but that a second test was negative.
Iraqi and Kurdish forces, backed by the US -led coalition, are said to be developing a pincer strategy that would see Iraqi troops advancing from the southeast and Kurdish units coming from the northwest.
He added that Iraqi forces were moving into a tactical assembly area in preparation for the assault.
Al Jazeera quoted the chairman of the Joint Chiefs of Staff in the Iraqi-U.S. coalition general Joe Dunford that "We assess today that the Iraqis will have in early October all the forces marshalled, trained, fielded, equipped that are necessary for operations in Mosul". Gen. Joe Votel, who heads U.S. Central Command, said last month there may be areas Islamic State decides to cede to coalition forces immediately, and others in which it decides to fight to the death.
The Obama administration has maintained that ground troops in Iraq are not engaging in direct combat, but are serving in advise-and-assist roles to local forces.
US-led coalition warplanes last week destroyed a factory near Mosul suspected of being used by IS to make chemical weapons.
The new deployment, as with the previous few, would have the troops sent to Qayara Air Base, which Iraqi forces occupied back in July.
No one was injured in the rocket attack on Tuesday on Qayyarah, the US' de facto base outside the Isis stronghold of Mosul.
This marks the first recorded chemical attack on the United States since the jihadist group conquered swaths of Iraq in 2014.
Assisted by our friends in the worldwide community, we started to implement programs for the return of internally displaced people (IDPs) to their liberated areas, where we developed an integrated program for re-stabilization and service provision, particularly water, electricity, schools and hospitals.
Backed by US -led coalition airstrikes and paramilitary forces, Iraqi government troops on Thursday pushed Islamic State militants from a key town north of the Iraqi capital, days after starting an operation to retake it, a military spokesman said.