The United States and its allies have completed a 12-year military operation against the Islamic State group in Iraq, Chief Pentagon spokesman Sean Parnell said in a statement on Wednesday.

"The orderly departure of Coalition forces and equipment from Erbil Air Base marks the successful conclusion of the military mission that defeated ISIS in Iraq",  said the statement.

The Iraqi Security Forces, including the Peshmerga and other security forces in the Iraqi Kurdistan Region, are expected to lead the continuing effort to secure Iraq and keep ISIS remnants suppressed. 

US Department of War will continue to provide targeted training and intelligence support to its Iraqi partners, according to the statement.

In 2014, ISIS seized vast territories across Iraq's west and north. The US-led coalition to combat the extremist group was subsequently formed and deployed forces to Iraq.