Turkish Prime Minister Binali Yildirim (R) talks with US Vice President Joe Biden (L) at Cankaya Palace in Ankara, on August 24, 2016. US Vice President Joe Biden arrived in Ankara to meet Erdogan, with agreeing a unified strategy on Syria set to be a crucial issue. Biden is likely to face expressions of alarm from Turkey about the activities inside Syria of the People's Protection Units (YPG) militia, which Washington sees as an ally but Ankara regards as a terror group. / AFP PHOTO / TURKISH PRIME MINISTRE PRESS OFFICE / HO / RESTRICTED TO EDITORIAL USE - MANDATORY CREDIT "AFP PHOTO / TURKISH PRIME MINISTER PRESS OFFICE / HAKAN GOKTEPE" - NO MARKETING - NO ADVERTISING CAMPAIGNS - DISTRIBUTED AS A SERVICE TO CLIENTS HO/AFP/Getty Images

TOPSHOT - US President Barack Obama exits Marine One upon arrival on the South Lawn of the White House in Washington, DC, August 23, 2016, after traveling to Baton Rouge, Louisiana, to tour flood damage. / AFP PHOTO / SAUL LOEBSAUL LOEB/AFP/Getty Images

WASHINGTON, DC - AUGUST 23: US President Barack Obama waves as he steps off of Marine One as he returns to the White House on August 23, 2016 in Washington, D.C. The president spent the day viewing flood damage and the rebuilding efforts in Baton Rouge, Louisiana. (Photo by T.J. Kirkpatrick-Pool/Getty Images)

WASHINGTON, DC - AUGUST 23: Marine One lands on the South Lawn as President Barack Obama returns to the White House on August 23, 2016 in Washington, D.C. The president spent the day viewing flood damage and the rebuilding efforts in Baton Rouge, Louisiana. (Photo by T.J. Kirkpatrick-Pool/Getty Images)

WASHINGTON, DC - AUGUST 23: US President Barack Obama steps out from Marine One as he returns to the White House on August 23, 2016 in Washington, D.C. The president spent the day viewing flood damage and the rebuilding efforts in Baton Rouge, Louisiana. (Photo by T.J. Kirkpatrick-Pool/Getty Images)

WASHINGTON, DC - AUGUST 23: US President Barack Obama greets the family of a Marine One pilot as he returns to the White House on August 23, 2016 in Washington, D.C. The president spent the day viewing flood damage and the rebuilding efforts in Baton Rouge, Louisiana. (Photo by T.J. Kirkpatrick-Pool/Getty Images)

WASHINGTON, DC - AUGUST 23: US President Barack Obama walks away from Marine One as he returns to the White House on August 23, 2016 in Washington, D.C. The president spent the day viewing flood damage and the rebuilding efforts in Baton Rouge, Louisiana. (Photo by T.J. Kirkpatrick-Pool/Getty Images)

WASHINGTON, DC - AUGUST 23: US Marine One lands on the South Lawn as President Barack Obama returns to the White House on August 23, 2016 in Washington, D.C. The president spent the day viewing flood damage and the rebuilding efforts in Baton Rouge, Louisiana. (Photo by T.J. Kirkpatrick-Pool/Getty Images)