The United States criticized clashes between Turkish forces and some opposition groups in northern Syria on Monday as "unacceptable" and called on all armed actors in the fighting to stand down and focus on the fight against Islamic State (IS).

“We want to make clear that we find these clashes – in areas where ISIL is not located – unacceptable and a source of deep concern” Brett McGurk, the special presidential envoy for the coalition to counter IS, said on his official Twitter account, citing a defense department statement.

“We call on all armed actors to stand down… the U.S. is actively engaged to facilitate such deconfliction and unity of focus on ISIL [IS], which remains a lethal and common threat.”

Turkey and its Syrian rebel allies seized territory controlled by Kurdish-aligned forces on Monday, the fifth day of a cross-border campaign. The YPG fighters are backed by the United States in the fight against IS in Syria.