The nearly eight-year-old US deployment to Syria to combat ISIS is still worth the risk, the top US military officer said on Saturday, after an unannounced visit to a base to meet US troops in the country’s northeast, Reuters reported.

Army General Mark Milley, chairman of the Joint Chiefs of Staff, flew to Syria to assess efforts to prevent a resurgence of the militant group and review safeguards for American forces against attacks, including from drones.

While ISIS is a shadow of the group that ruled over a third of Syria and Iraq in a so-called “Caliphate” declared in 2014, hundreds of fighters are still camped in desolate areas where neither the US-led coalition nor the Syrian army, with support from Russia and Iranian-backed militias, exert full control.

Thousands of other ISIS extremists are in detention facilities guarded by Kurdish-led Syrian Democratic Forces, America’s key ally in the country.

American officials say that ISIS could still regenerate into a major threat.

Asked by reporters traveling with him if he believed the Syria mission was worth the risk, Milley tied the mission to the security of the United States and its allies, saying: “If you think that that’s important, then the answer is ‘Yes.'”

“I happen to think that’s important,” Milley said.

“So I think that an enduring defeat of ISIS and continuing to support our friends and allies in the region … I think those are important tasks that can be done.”

The mission carries risk. Four US troops were wounded during a helicopter raid last month when an ISIS leader triggered an explosion.

Last month, the US military shot down an Iranian-made drone in Syria that was attempting to conduct reconnaissance on a patrol base in northeastern Syria.

Three drones targeted a US base in January in Syria’s Al-Tanf region. The US military said two of the drones were shot down while the remaining drone hit the compound, injuring two members of the Syrian Free Army forces.

US officials believe the attacks are being directed by Iran-backed militia.

US Army Major General Matthew McFarlane, who commands the US-led coalition against ISIS in Iraq and Syria, described the attacks as a “distraction from our main mission.”

McFarlane cited progress against ISIS, including through the reduction in the numbers of internally displaced people at refugee camps — a pool of people who could be recruited by ISIS.

He also noted ongoing operations against the remnants of ISIS.

“Our number one priority is the enduring defeat of ISIS. And we are making progress,” he said.