Turkey is stepping up humanitarian aid to northernIraq, officials said on Friday, but looks unlikely to get involved in military action against advancing Islamist militants there unless its southern border with Iraq is directly threatened.

Turkey has a 370-km (230-mile) border with Iraq and has been alarmed by the advance of Islamic State fighters towards Arbil, capital of the Iraqi Kurdish region which has until now served as a buffer for Turkey against the instability further south.

U.S. warplanes struck Iraq on Friday for the first time since American troops pulled out in 2011, hitting a mobile artillery piece used by the Sunni militants to shell Kurdish forces defending Arbil. […]