American-led forces have sharply intensified air strikes in the past two days against Islamic State fighters threatening Kurds on Syria's Turkish border after the jihadists' advance began to destabilize Turkey, Reuters reported.

The coalition had conducted 21 attacks on the militants near the Syrian Kurdish town of Kobani over Monday, Oct 13 and Tuesday and appeared to have slowed Islamic State advances there, the U.S. military said, but cautioned the situation remained fluid.

U.S. President Barack Obama voiced deep concern about the situation in Kobani as well as in Iraq's Anbar province, which U.S. troops fought to secure during the Iraq war and is now at risk of being seized by Islamic State militants.

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.

The plight of the Syrian Kurds in Kobani provoked riots among Turkey's 15 million Kurds last week in which at least 35 people were killed.