The reinforcements arrived after U.S. President Donald Trump on Wednesday announced he was pulling all 2,000 U.S. troops out of Syria, Time reported.

The Britain-based Syrian Observatory for Human Rights said the government sent thousands of its elite forces to Deir al-Zur that borders Iraq, where IS holds the last area under its control in Syria.

The Observatory said the troops and pro-government fighters were deployed on the west banks of the Euphrates River close to the IS-held enclave, mostly in the towns of Mayadeen and Boukamal. It added that troops brought to the area include members of the Tiger Force, an elite unit that defeated rebels and IS gunmen on several fronts over the past two years.

A pro-government Facebook page posted a photo of Tiger Force commander Brig. Gen. Suheil and also reported that troops under his command have arrived in Deir al-Zur. It also posted photos of military vehicles said to be arriving in the area.

U.S.-backed Syrian fighters of the Kurdish-led Syrian Democratic Forces have been trying to capture the area from IS since Sept. 10. The battles have left hundreds of IS and SDF fighters dead.

On Friday, senior Kurdish politician Ilham Ahmed warned in Paris that SDF fighters may have to withdraw from the front lines in the fight against IS to deploy along the borders with Turkey after Ankara said it plans to carry an attack.

The Observatory’s chief, Rami Abdurrahman, said the troops were deployed for a possible attack on IS or to assume control of areas that could be evacuated by SDF fighters.

In Washington, Brett McGurk, the U.S. envoy to the global coalition fighting IS, has resigned in protest to Trump’s abrupt decision to withdraw U.S. troops from Syria, joining Defense Secretary Jim Mattis in an administration exodus of experienced national security officials.

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