Airstrikes carried out by the U.S. military this week against several Islamic State targets in Syria highlight concerns about the terror group's growing presence in the war-torn country, experts say.

U.S. Central Command, or CENTCOM, said Wednesday that its forces had conducted strikes on Monday targeting multiple camps belonging to IS, or ISIS, in the Syrian desert. Nearly 35 IS operatives, including senior leaders, were killed in the airstrikes, the U.S. military said.

Despite its territorial defeat in 2019, IS has been carrying out attacks through sleeper cells across Iraq and Syria. In recent months, militants affiliated with the group have increasingly become active in areas controlled by forces loyal to the government of Syrian President Bashar Assad and their Iranian and Russian allies.

The Syrian Desert, also known as the Badia, where the U.S. forces struck IS positions this week, has seen a significant surge in violence by IS militants in recent months.

IS had maintained training camps in the Syrian desert for many years, according to Gregory Waters, a research analyst at the Counter Extremism Project who closely follows IS activities in central Syria.

"These are the places where it trains the next generation of fighters — often children it recruits from northeast Syria — and where adult fighters can return to in between their operations," Waters told VOA. "While the central Syrian desert is under Russian and Syrian regime control, ISIS does not abide by these arbitrary lines."

He added that IS cells in the central desert support the cells operating in northeast Syria, which is largely under the control of U.S.-backed and Kurdish-led Syrian Democratic Forces, or SDF.

The United States has about 900 troops in northeast Syria as part of a global coalition against IS.

"Oftentimes the fighters will cross from one region to the other to either conduct attacks or to escape from counter-ISIS operations," Waters said.

Colin Clarke, director of research at The Soufan Group, said the U.S. strikes demonstrate that the terror group remains a significant threat in Syria.

"Moreover, the Assad regime lacks either the will or the capability to counter ISIS, so the United States has remained vigilant in its efforts to keep the group on the defensive," he told VOA.

"Any time you have a terrorist group with the legacy of the Islamic State, with a proven track record of being able to recruit, plan and conduct attacks, including external operations in the West, it is never a good idea to become complacent," Clarke said. "The strikes are necessary to keep ISIS from regrouping, whether in Syria or the hinterlands of Afghanistan."

Abdul Wahab Assi, a researcher at the Istanbul-based Jusoor Center for Studies, said the U.S. strikes in the Syrian Desert carried a political message, as well.

"It sent a message to Russia, which ostensibly operates against IS in that particular area, that it's not doing enough" to counter IS activities in Syria, he told Syria TV, a news channel affiliated with the Syrian opposition.

Last week, Iraqi Prime Minister Mohammed Shia al-Sudani announced the killing of the IS leader in Iraq and eight other senior IS commanders in a joint operation by U.S. and Iraqi forces.

CENTCOM said in its Wednesday statement that alongside its allies and partners in the region, it "will continue to aggressively degrade ISIS operational capabilities to ensure its enduring defeat."

This story originated in VOA's Kurdish Service.