Cool reception awaits Erdogan in Washington

Turkish President Recep Tayyip Erdogan was to attend a two-day nuclear security summit being held in the US capital at a time of fraught relations between Ankara and Washington and questions about whether the countries' leaders would even meet.

Disagreements between two key NATO allies have been increasing amid growing differences on policies towards Syria, a rebel Kurdish faction and Turkey's clampdown on the free press.

Whereas rooting out Islamic State (IS) militants in Syria and Iraq is Washington's priority, Erdogan has appeared more keen to topple Syrian strongman Bashar al-Assad. To its end of fighting IS, the US has developed ties with the Democratic Union Party (PYD) rebels in Syria, who have proven to be reliable partners in combat.

Turkey considers the PYD to be partners of the outlawed Kurdistan Workers Party (PKK), a separatist group seeking to carve out an autonomous Kurdish state across Turkey, Syria, Iraq and Iran.

"The relationship between the US and Turkey is strained generally because of the differing priorities of the two allies in Syria and more specifically due to their perceptions of the PYD," said Ozgur Unluhisarcikli, Ankara Office Director of the German Marshall Fund of the United States.

He said Turkey and the United States were "stepping on each other's toes" in Syria.

"Until either or both of the sides revise their approach to PYD, the US-Turkey relationship will continue to be poisoned by this issue," he said.

Crackdown on the free press

Turkey's relations with the US, as well as European allies, have also been strained by Ankara's clamp down on the free press.

Earlier this month the Turkish government seized control of the country's largest newspaper - Zaman. And just last week he lashed out at western diplomats for attending the opening of a treason trial against two journalists from the Cumhuriyet newspaper.

Erdogan called the diplomats' presence at the trial interference in the country's internal affairs.

Tweets by the US embassy supporting prosecuted academics and journalists have made Ambassador John Bass a hated figure among Turkish hardliners.

US State Department spokesman John Kirby effectively shrugged, "We don't always agree on everything - media freedom is one of them," he said.

Besides the security summit, Erdogan will preside over the grand opening of a large Ottoman-style mosque in Maryland. He had hoped to be joined at the event by US President Barack Obama, but the White House declined.

Before departing Turkey Erdogan said he would meet with Obama during his visit to Washington, but it now appears that he will meet with Vice-President Joe Biden.