U.S. airstrikes killed nearly 150 Islamic State militants near Al-Shafah, Syria, on Saturday, officials with Operation Inherent Resolve announced.

The precision strikes targeted an ISIS headquarters and command and control center in the Middle Euphrates River Valley, according to a Tuesday press release.

A heavy concentration of 145 to 150 ISIS fighters who appeared to be “massing for a movement” were killed in the strikes, officials said.

“The strikes underscore our assertion that the fight to liberate Syria is far from over,” said Army Maj. Gen. James Jarrard, commanding general of Special Operations Joint Task Force – Operation Inherent Resolve.

The Syrian Democratic Forces — a primarily Kurdish alliance of U.S.-backed fighters — provided target observation and intelligence to aircraft prior to the airstrike, according to the press release.

The SDF fighters provided continuous eyes on the target, ensuring there were no accidental engagements of civilians, officials said.

Members of the SDF continue to engage in heavy fighting against ISIS holdouts attempting to regroup in the region.

“Our SDF partners are still making daily progress and sacrifices, and together we are still finding, targeting and killing ISIS terrorists intent on keeping their extremist hold on the region,” Jarrard said. “We cannot take our focus off our mission, and we must not lose our momentum in taking these terrorists off the battlefield and preventing them from resurfacing somewhere else.”

The Islamic State has lost more than 98 percent of the territory it once claimed as part of its caliphate, officials said. However, the group has continued to mass in large numbers as they search for a new foothold in Syria.

The Euphrates River Valley, where the strike took place, has become a strategic linchpin in ISIS’ attempts to recoup territory.

Regaining control of the area would be vital for Syria to rebuild in a post-ISIS environment, according to James Phillips, a senior research fellow for Middle Eastern affairs at the Heritage Foundation.

"Many of the important Sunni towns are located in the valley," Phillips said in June.

Within Syria, "the Euphrates Valley is a very important communications and transportation vector," Phillips said.

That reality appears to be informing the U.S.-led coalition’s commitment to continue strikes against ISIS encampments.

“The continued discovery of ISIS concentrations and facilities reinforces the coalition’s commitment to achieving the lasting defeat of ISIS,” the press release states.