Turkey’s air and ground “Operation Olive Branch” in the Afrin region of northern Syria is now in its fifth day, targeting Kurdish YPG fighters and opening a new front in Syria’s multi-sided civil war.

A push toward Manbij, in a separate Kurdish-held enclave some 100 km (60 miles) east of Afrin, could threaten U.S. plans to stabilize a swath of northeast Syria.

The United States has around 2,000 special forces troops in Syria, officially as part of an international U.S.-led coalition, assisting the Kurds in battle against Islamic State.

None of the Americans are known to be based in the Afrin area, but they are deployed in the Kurdish-held pocket that includes Manbij. Washington has angered Turkey by providing arms, training and air support to the Syrian Kurdish forces, which Turkey considers enemies.

“With the Olive Branch operation, we have once again thwarted the game of those sneaky forces whose interests in the region are different,” Erdogan said in a speech to provincial leaders in Ankara.

“Starting in Manbij, we will continue to thwart their game.”

U.S. President Donald Trump plans to raise the U.S. concerns over the Turkish offensive in a telephone call with Erdogan expected on Wednesday, a senior U.S. official said.

In an interview with Reuters, Turkey’s government spokesman said he saw a small possibility that Turkish forces could come face-to-face with the U.S. troops in Manbij.

Reporter’s code: 50101