American-led forces sharply intensified air strikes against Islamic State fighters threatening Kurds on Syria’s Turkish border on Monday and Tuesday after the jihadists’ advance began to destabilize Turkey.

The coalition had conducted 21 attacks on the militants near the Syrian Kurdish town of Kobani over the past two days and appeared to have slowed Islamic State advances there, the U.S. military said, but cautioned that the situation remained fluid.

War on the militants in Syria is threatening to unravel a delicate peace in neighboring Turkey where Kurds are furious with Ankara over its refusal to help protect their kin in Syria. […]