The United States and its NATO allies denounced Russia on Monday for violating Turkish air space along the frontier with Syria, and Ankara threatened to respond if provoked again, raising the prospect of direct confrontation between the Cold War enemies. NATO held an emergency meeting of ambassadors of its 28 member states to respond to what Secretary-General Jens Stoltenberg called "unacceptable violations of Turkish air space" after Turkey said a Russian jet had crossed its frontier. NATO members "strongly protest" and "condemn" incursions into Turkish and NATO territory, the alliance said. "Allies also note the extreme danger of such irresponsible...