WASHINGTON (AFP) - US President Donald Trump spoke by telephone on Saturday (Sept 9) with Turkish President Tayyip Erdogan and discussed working more closely with its Nato ally to improve regional security, the White House said.

"President Trump emphasised the common commitment of the United States and Turkey to work together to increase regional stability," a White House statement said.

The phone call came amid a backdrop of deteriorating relations between Washington and Ankara, Nato allies whose relations have soured over the US decision to arm Kurds in Syria to fight Islamic State.

Turkey regards the Kurdish militias as "terrorists."

Turkey has also repeatedly demanded, without success, that the United States extradite Fethullah Gulen, a Turkish preacher who lives in Pennsylvania and is accused by Ankara of being behind a failed coup against Erdogan in July 2016.

US authorities have also charged several Turks with violating financial sanctions against Iran, including former economy minister Zafer Caglayan.

Erdogan denounced the charges as a politically-motivated decision against Turkey.

But he has said that, if the opportunity arises, he will meet with Trump on the sidelines of the UN General Assembly, which begins Sept 19 in New York.