WASHINGTON — The U.S. military has carved out a new role in Syria, with small numbers of troops now positioned to prevent an escalation of violence among an array of militias and other forces that have converged on an increasingly complex battlefield.

A Pentagon spokesman, Navy Capt. Jeff Davis, on Monday said the U.S. troops are on the western outskirts of Manbij to "reassure and deter," and are making themselves visible by flying American flags. It is neither an offensive nor defensive role, he said, but a mission designed to keep a lid on tensions that risk creating new levels of violence in northern Syria.

"It's a visible reminder, for anybody who's looking to start a fight, that the only fight that should be going on right now is with ISIS," Davis said, using the Trump administration's preferred acronym for the Islamic State group.

Manbij is a flashpoint because Turkey claims that Syrian Kurdish fighters it considers a threat to Turkey are operating in the city, despite U.S. denials. Also in the area are Syrian regime forces backed by Russia as well as American-supported Syrian Arab fighters.

The "reassure and deter" mission, as described by Davis, does not reflect a fundamental shift in the U.S. approach to combating ISIS in Syria. It appears to have emerged as an improvised way to prevent the Syrian conflict from escalating and to keep Turkish and Syrian opposition groups focused on fighting ISIS rather than each other. Davis said the deployment of small numbers of U.S. troops in and around Manbij was done under authorities that existed prior to U.S. President Donald Trump taking office in January and therefore did not require new approvals in Washington.

Asked whether this is a new mission for U.S. troops in Syria, Davis said: "It is, absolutely." He said the deployments are temporary.

The spokesman said the new U.S. presence is meant in part to "reassure that ISIS has been driven from Manbij," adding: "Manbij is liberated and there's not a need for further fighting there." He did not mention Turkey, but the Turkish government has insisted that Kurds are still in Manbij and that it intends to eject them by force if necessary.

Asked whether the "reassurance" is aimed at Turkey, Davis said, "We're concerned about anybody who views Manbij as needing to be liberated." He added, "I'll let you draw your conclusions" who that might be, among the foreign forces involved there.

He declined to say how many U.S. troops are involved, but said they are small in number — fewer than "dozens." They are in addition to an undisclosed number of U.S. special operations troops who have been working inside Manbij for months to help a local coalition, known as the Manbij Military Council, to hold the city and restore governance.

The volatile situation in and around Manbij is worrisome for the U.S. on several levels, including a concern that additional conflict there could detract from U.S. efforts to mold a Syrian opposition force capable of recapturing Raqqa, the ISIS self-declared capital. The U.S. wants to include Kurds in that offensive, but Turkey strongly opposes their involvement.

Syrian regime forces and their Russian partners represent an additional layer of complexity.

Army Lt. Gen. Stephen Townsend, the commander of U.S. and coalition forces in Syria and Iraq, said last Wednesday that within the previous two days Syrian regime forces had advanced to "essentially rifle-range or hand-grenade range" of U.S.-backed Syrian Arab Coalition fighters who are holding the area around Manbij. "It's very difficult and very complicated," Townsend said.

The White House, in consultation with Defense Secretary Jim Mattis, is considering options for accelerating the fight against ISIS militants in Syria. Key to that decision is the role of Turkey and the Syrian Kurdish force known as the YPG. The Pentagon considers the YPG its most effective local partner in Syria and has suggested arming them directly, despite Turkish government opposition.

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