U.S.-led coalition and its Syrian partners killed more than 20 Islamic State fighters and captured 17 others Wednesday in fighting outside U.S. base at Tanf, the coalition said Thursday.

It was the second combat action around that key US base and coalition officials took issue with what they described as ISIS has been able to move freely through Syrian regime-controlled territory with a Russian military presence.

Despite the presence of Russian-backed, pro-Syrian regime forces in the area, Daesh still finds ways to move freely through regime lines and pose a threat,” coalition director of operations Brig. Gen. Jonathan Braga said in the statement, using an alternate name for ISIS. “We shall continue to work by, with and through our partner forces to deny Daesh the ability to regroup and reorganize.”

Given its location, the base has been seen as an important outpost as the United States, Russia and Iran jockey for influence in the region. Iran in particular is said to want to control a route running from Iran to the Mediterranean that would runs through that area.