U.S. forces conducted a series of strikes in far eastern Syria that killed as many as 150 suspected Islamic State militants, the U.S. military said this week.

The operation took place on Saturday in the town of As Shafah, near the Iraqi border, the U.S.-led military coalition said in a statement.

A defense official, speaking on the condition of anonymity to discuss details of what occurred, said officials had observed the site for more than a week before the attack. It was believed to be a "command and control" location for the group, which has been pushed out of major urban centers in Iraq and Syria but remains a potent force in isolated areas.

The strike, with its high death toll, comes several months after Syrian government forces recaptured Bukamal, a border town a short distance from As Shafah. Government officials depicted that battle as a major milestone against the Islamic State, even as the larger Syrian conflict grinds on.

After a years-long intensive air campaign, the U.S. military has scaled back the pace of strikes against the Islamic State in Syria, but attacks continue on remaining militant strongholds along the Euphrates River.

In its statement, the coalition said that Syrian partner forces helped monitor the location in As Shafah before the strikes.

While officials said that the suspected militants in As Shafah appeared to be "massing for movement," they did not have a clear explanation for why so many would gather in a single location, given that large groupings have been frequent targets for airstrikes.

Neither was it clear where they might have been preparing to go.

The official said some fighters, who are believed to number about 1,000 across Iraq and Syria, had been attempting to flee areas where militants are subject to attack from the Syrian government or the U.S.-led coalition.

He said those targeted were "purely ISIS fighters," using an acronym for the group.

The Trump administration has been seeking to counter allegations that intense strikes in 2017 resulted in thousands of civilian casualties.