The chairman of the Joint Chiefs of Staff, Gen. Mark Milley, said Sunday about 500 or 600 US troops will remain in Syria to counter ISIS militants. President Donald Trump recently approved an expanded military mission to secure oil fields across eastern Syria. His decision locked hundreds of US troops into a more complicated presence in Syria despite his pledge to bring them home. Milley told ABCs "This Week" that pressure must be maintained on ISIS militants still in the region. "There are still ISIS fighters in the region. And unless pressure is maintained, unless attention is maintained on that group, then there is a very real possibility that conditions could be set for a reemergence of ISIS," he said in his first interview since taking his role as chairman of the Joint Chiefs of Staff. "If I do my math and I look at the new troops going in and those going out, it could be more than 700 who remain," said "This Week" co-anchor Martha Raddatz. Milley responded: "Well, therell be less than a thousand for sure, and probably in the 500-ish frame, maybe six. But its in, that its in, that area. But were not gonna go into specific numbers because were still going through the analysis right now." Its unclear whether Milleys prediction of keeping 500 to 600 American troops there includes the roughly 200 who are at the al-Tanf garrison in southern Syria.