(From L) Turkish Prime Minister Binali Yildirim (L), US Vice President Joe Biden (C) and Turkish Foreign Minister Mevlut Cavusoglu (R) walk 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 / HAKAN GOKTEPE / 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 HAKAN GOKTEPE/AFP/Getty Images