American and Western intelligence and counterterrorism officials say, however, that the Islamic State’s defeat on the ground in Syria and Iraq, and a growing shadow war against the group’s branches in West Africa to Afghanistan, has failed to stifle its ability to mobilize a potent global following through social media.

“ISIS’s online messaging has multiple themes, and if battlefield losses force the group to shift away from messages emphasizing the holding of territory, the group can pivot toward its claim to victimhood,” Joshua A. Geltzer, a former senior director for counterterrorism at the National Security Council in the Obama administration, said in congressional testimony last week.

The shifting tactics come at a time when the Islamic State has been able to reclaim some territory, particularly west of the Euphrates River, in area controlled by the Syrian army and its Russian military patrons. Islamic State fighters have conducted more attacks on the western side of the Euphrates against forces aligned with the government of President Bashar al-Assad, American and other western analysts said.

This past weekend, at least four Russian soldiers working with Syrian army troops were killed and five others wounded in a nighttime attack by Islamic State fighters in eastern Deir al-Zour province.

“We remain concerned that the Syrian regime is either unwilling or unable to deal with that threat,” Maj. Gen. Felix Gedney of Britain, another deputy commander of the allied operations in Iraq and Syria, told the BBC last week.

Even if the last militant holdouts are captured or killed, American officials and analysts acknowledged that a plan to ensure security and stability in the region remains elusive.

“What is the U.S.’s political approach in eastern Syria, including around the Middle Euphrates River Valley? Who will govern these areas?” said Mr. Jones of the strategic studies center. “These questions are critical since successful counterterrorism and counterinsurgency campaigns have always required strong, competent governments. Weak, failed states are not a recipe for success.”


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Battle to Stamp Out ISIS in Syria Gains New Momentum, but Threats Remain