Nearly 150 Islamic State fighters were killed during U.S.-led coalition airstrikes targeting IS headquarters in eastern Syria late last week, the coalition said in a statement.
The strikes on Saturday targeted a congregation of IS fighters near the town of as-Shafah in eastern Syria's contested Middle Euphrates River Valley, the coalition statement said Tuesday. The fighters, heavily concentrated, were apparently massing for movement.
"The strikes underscore our assertion that the fight to liberate Syria is far from over," the commander of special operations for the coalition, Major General James Jarrard, said in the statement.
The U.S. has signaled an open-ended military presence in Syria as part of a broader strategy to prevent a resurgence of IS, pave the way diplomatically for the eventual departure of Syrian President Bashar al-Assad and curtail Iran's influence.
IS has yet to confirm Saturday's airstrikes, but its Amaq News Agency claimed 14 people, including seven women, were killed during a coalition strike targeting as-Shafah hospital on Tuesday.
The coalition statement said Saturday's strikes were conducted with assistance from the U.S.-backed Syrian Democratic Forces, which include Kurdish YPG fighters who provided target observation about IS.
"The combination of intelligence and continuous eyes on the target ensured no accidental engagement on nonmilitary personnel," the coalition statement said.
"We cannot take out focus off our mission, and we must not lose out momentum in taking these terrorists off the battlefield and preventing them from resurfacing somewhere else," Jarrard said.
The strikes on Saturday came as the U.S. urged Turkey to show restraint in its campaign against Kurdish forces in northern Syria and to focus on fighting the Islamic State. On Tuesday, Turkey claimed to have killed 260 Kurdish and IS fighters in a four-day offensive the north of the country.
Turkey is engaged in an air and ground offensive in northwestern Syria's city of Afrin against a Kurdish group known as People's Protection Units, or YPG. The group is the backbone of the SDF and a key ally of the U.S. in its current fight against IS in the region.
Turkey alleges the YPG is an extension of the banned Kurdistan Workers' Party, which has been fighting for Kurdish autonomy in Turkey for decades. The YPG denies those accusations.
The United States has led an international coalition conducting airstrikes against Islamic State since 2014. U.S. troops have served as advisers on the ground with Iraqi government forces and with Kurdish and Arab groups in Syria.
The coalition has said in the past that fewer than 1,000 IS fighters remain in Iraq and Syria, but that the militant group still remains a threat. The figure excludes areas in western Syria under the control of Assad's government and his allies.
Nisan Ahmado contributed to this report.