US seeks to soothe Turkey ties, press fight against Islamic State

But his tone was markedly different when he arrived in Ankara on August 24 weeks after a failed coup in Turkey that has strained relations between the two countries, and he appeared to be in diplomatic damage-limitation mode.

Turkish officials have been incensed by the concerns expressed by Washington and European capitals about Ankara's subsequent crackdown on suspected plotters, but what they perceive as indifference to the coup attempt itself.

A weakening of the US-Turkish alliance is a concern for the United States, which is counting on support from Turkey - which has NATO's second-biggest military - in the battle against Islamic State.

American worries may have been compounded by Erdogan restoring ties with Russia and even discussing military cooperation with President Vladimir Putin.

Meeting with Erdogan and Turkey's prime minister in Ankara on August 24 Biden delivered a message of alliance and conciliation.

Hours before Biden arrived, in a timely illustration of the role Turkey plays in the fight against Islamic State, Turkish forces backed by US-led coalition jets launched a major push across the border into northern Syria to drive the jihadist group out of the frontier town of Jarablus.

Since the attempted coup - in which more than 240 people were killed - Turkish authorities have dismissed or suspended tens of thousands of military personnel, civil servants and judges suspected of ties to Gulen's network. Around 40,000 people have been formally arrested for links to the coup.