WASHINGTON (REUTERS) - The United States on Sunday (Jan 21) urged North Atlantic Treaty Organization ally Turkey to"exercise restraint" and limit its military operations in northwestern Syria, where Turkish forces are attacking a US-backed Kurdish militia they aim to sweep from the border.

US Secretary of State Rex Tillerson spoke by phone with his Turkish and Russian counterparts on Saturday (Jan 20) to express concern about the situation, State Department spokeswoman Heather Nauert said in a statement.

While supporting Ankara's legitimate security concerns, "we urge Turkey to exercise restraint and ensure that its military operations remain limited in scope and duration and scrupulous to avoid civilian casualties," Nauert said.