WASHINGTON — The U.S. is talking multiple times a day with Russia to deconflict ground and air operations in Syria, according to Gen. Stephen Townsend, commander of the U.S.-led coalition against ISIS in Iraq and Syria.

The fight for Raqqa, the Islamic State’s de facto capital continues, but with the liberation of Mosul, Iraq, and the stunningly swift defeat of the militants in Tal Afar, the next stepping stone in the battle against ISIS will be the middle Euphrates River valley, from Deir ez-Zor, about 80 miles southeast of Raqqa, to the Iraqi border. Thousands of ISIS fighters have entrenched themselves there, fleeing from the coalition onslaught.

“The last stand of ISIS will be in the MERV,” said Townsend, referring to the valley.

The battlespace along the Euphrates River is tightly congested and “fraught with friction” between competing forces, Townsend said.

Syrian regime forces backed by Russia, and various regime-supported proxies, are operating just south of Tabqa, the site of a large dam along the Euphrates about 20 miles west of Raqqa.

“We are trying to deconflict this,” Townsend said during a televised Pentagon press briefing Thursday.

Russia and the coalition have agreed to some deconfliction lines in the middle Euphrates River valley,” Townsend said, but he added that “not all of it yet” has been decided.

Previously, the communication hotline between the coalition and Russia was largely devoted to air deconfliction, to help avoid midair collisions in the congested airspace over Syria.

However, during recent campaigns to liberate the cities of al-Bab and Tabqa, in which unfriendly forces converged, it became clear that there needed to be a ground component to the deconfliction hotline with Russia, Townsend said.

“It gets tougher [to communicate] with a force that isn’t friendly but not necessarily an adversary,” Townsend explained.

“Those rehearsals have allowed us to come up with measures that seem to work,” he said. “We were able to work through that then.”

Between air and ground deconfliction, “someone is talking to the Russians multiple times a day,” Townsend said. “It’s a fact of life.”