The US military has completed the withdrawal of American forces and equipment from Erbil Air Base in Iraq, ending its Operation Inherent Resolve mission, US Central Command announced Wednesday.

The departure closes the Iraq chapter of the U.S.-led military mission launched against ISIS in 2014, while shifting primary responsibility for the country's security to Iraqi forces. The broader counter-ISIS campaign is not ending, however, with the U.S.-led task force relocating its headquarters to Jordan and operations continuing in Syria.

"Job well done to the tens of thousands of American service members, diplomats, and civilian personnel who answered the call in Iraq," CENTCOM commander Adm. Brad Cooper said.

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"Because of your grit, sacrifice and professionalism, ISIS no longer poses a systemic threat to Iraq’s national security and Iraqi security forces, including the Peshmerga and other Iraqi Kurdistan Region security forces, now possess the capacity, leadership, and operational independence to unilaterally manage threats to their homeland."

Erbil Air Base in northern Iraq served as the main operational hub for Combined Joint Task Force-Operation Inherent Resolve and hosted most of the roughly 1,500 American and Coalition forces supporting counter-ISIS operations, according to CENTCOM.

U.S. and Coalition forces began leaving federal Iraq last October as Washington and Baghdad moved toward a bilateral defense relationship. The final removal of personnel and equipment from Erbil completed that transition on Sept. 30.

Combined Joint Task Force-Operation Inherent Resolve remains active and is now headquartered in Jordan, according to CENTCOM. U.S. forces also continue counter-ISIS operations in Syria alongside Coalition partners and the Syrian government.

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"As we step back and hand full primary responsibility for Iraq’s security to the Government of Iraq and the brave people of Iraq, U.S. and Coalition forces stationed across the region will remain ready to respond to any ISIS threats that arise," Cooper said.

"Maintaining our vigilance and readiness is essential to protecting the U.S. homeland and strengthening regional security," he added. 

The withdrawal ends a U.S. military presence in Iraq that was reestablished in 2014, when Iraqi authorities sought international assistance as ISIS captured large areas of the country. U.S. troops had previously left Iraq in 2011 following the 2003 invasion that toppled Saddam Hussein.

The final departure comes as Iraq faces a separate security challenge from powerful Iran-backed militias operating inside the country. Baghdad has sought to bring weapons held by non-state groups under government control, but some of the most influential militias have resisted disarming.

The withdrawal has drawn sharply different reactions inside Iraq. Iran-aligned groups celebrated the U.S. departure, while officials in the country's Kurdish region have raised concerns about the loss of American air-defense capabilities amid drone and missile threats.

CENTCOM said U.S. and Coalition forces elsewhere in the region will remain prepared to respond if ISIS again poses a threat.

The Associated Press contributed to this report.