US President Barack Obama admitted Friday he was "troubled" by the path President Recep Tayyip Erdogan is taking Turkey down, amid rows over press freedom and the war in Syria.

"It's no secret that there are some trends within Turkey that I have been troubled with," Obama said, when asked whether he considers the Turkish leader an authoritarian.

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"I think the approach they have been taking toward the press is one that could lead Turkey down a path that would be very troubling."

Obama said he had expressed these sentiments to Erdogan "directly."

The pair met at the White House on Thursday for talks away from the cameras.

Erdogan was on a rare trip to Washington to take part in a major nuclear security summit with other world leaders.

Ahead of the trip, the White House had suggested Obama would not formally meet him, prompting suggestions of a snub.

The possibility of no meeting had been glaring -- the two countries are meant to be close NATO allies in the thick of a fight against the Islamic State group in Syria.

But tensions have been stirred by Ankara's attacks on Kurdish militants, some of whom are seen by Washington as the best bet for tackling IS fighters in Iraq and northern Syria.

Turkey says the groups are linked to the outlawed Kurdistan Workers' Party (PKK), which has fought a long battle for Kurdish independence and is seen by Ankara and Washington as a terrorist group.

Turkish forays into northern Iraq have also strained ties.

Before the meeting with Obama, there were ugly scenes when Erdogan gave a speech at the Brookings Institution, a Washington think tank.

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Ahead of his arrival, Turkish security officials clashed with protesters -- both sides exchanging insults and scuffling -- before police were able to separate them.

The Turkish guards also took aim at the press. One aimed a chest-high kick at an American reporter attempting to film the harassment of a Turkish opposition reporter while another called a female foreign policy scholar a "whore."

The US National Press Club accused Erdogan of trying to export oppression.