The U.S. military killed an ISIS leader and another member in an airstrike in Syria on Thursday, the Pentagon revealed Friday. U.S. Central Command (Centcom) Forces targeted Abu Yousef, also known as Mahmud, in the Dayr az Zawr Province, an area formerly controlled by the toppled regime of Bashar Assad and Russian fighters, it said in a statement. Another unidentified ISIS member was also killed in the strike, according to Centcom. “As stated before, the United States — working with allies and partners in the region — will not allow ISIS to take advantage of the current situation in Syria and reconstitute," Centcom Commander Gen. Michael Erik Kurilla said in the release. "ISIS has the intent to break out of detention the over 8,000 ISIS operatives currently being held in facilities in Syria. We will aggressively target these leaders and operatives, including those trying to conduct operations external to Syria." The airstrike came the same day it was revealed that there are 2,000 U.S. troops in Syria, more than double than the 900 previously publicly known to be in the war-torn country.  Pentagon press secretary Maj. Gen. Pat Ryder said that the increased force presence has “been going on for a while,” and that the troops have been there “at a minimum, months.” But he stressed the extra troops are supporting the counter-ISIS mission and were unrelated to the fall of Assad’s regime on Dec. 8. Ryder said a “core 900” U.S. service members are in Syria as part of an official nine- to 12-month deployment, while another 1,100 troops are there on a temporary basis for 30 to 90 days “to address shifting mission requirements.” The updated figure comes as the U.S. has increased its airstrikes on ISIS targets in Syria to prevent a resurgence of the group amid concerns of a power vacuum.