A handout picture taken and released on August 24, 2016 by the Turkey's President Press Service shows US Vice President Joe Biden (L) shaking hands with Turkish President Recep Tayyip Erdogan (R) at Turkish Presidential Complex in Ankara. US Vice President Joe Biden on August 24, 2016 said Washington had made clear that pro-Kurdish forces in Syria must not to cross west of the Euphrates River, a prospect alarming for Turkey. His comments come after Turkish troops launched an operation inside Syria to cleanse the key town of Jarabulus from Islamic State (IS) jihadists. / AFP PHOTO / TURKEY'S PRESIDENTIAL PRESS SERVICE / KAYHAN OZER / RESTRICTED TO EDITORIAL USE - MANDATORY CREDIT "AFP PHOTO / TURKEY'S PRESIDENTIAL PRESS SERVICE/ KAYHAN OZER- NO MARKETING NO ADVERTISING CAMPAIGNS - DISTRIBUTED AS A SERVICE TO CLIENTS KAYHAN OZER/AFP/Getty Images

A handout picture taken and released on August 24, 2016 by the Turkey's President Press Service shows US Vice President Joe Biden (L) shaking hands with Turkish President Recep Tayyip Erdogan (R) at Turkish Presidential Complex in Ankara. US Vice President Joe Biden on August 24, 2016 said Washington had made clear that pro-Kurdish forces in Syria must not to cross west of the Euphrates River, a prospect alarming for Turkey. His comments come after Turkish troops launched an operation inside Syria to cleanse the key town of Jarabulus from Islamic State (IS) jihadists. / AFP PHOTO / TURKEY'S PRESIDENTIAL PRESS SERVICE / KAYHAN OZER / RESTRICTED TO EDITORIAL USE - MANDATORY CREDIT "AFP PHOTO / TURKEY'S PRESIDENTIAL PRESS SERVICE/ KAYHAN OZER- NO MARKETING NO ADVERTISING CAMPAIGNS - DISTRIBUTED AS A SERVICE TO CLIENTS KAYHAN OZER/AFP/Getty Images

A handout picture taken and released on August 24, 2016 by the Turkey's President Press Service shows US Vice President Joe Biden (L) shaking hands with Turkish President Recep Tayyip Erdogan (R) at Turkish Presidential Complex in Ankara. US Vice President Joe Biden on August 24, 2016 said Washington had made clear that pro-Kurdish forces in Syria must not to cross west of the Euphrates River, a prospect alarming for Turkey. His comments come after Turkish troops launched an operation inside Syria to cleanse the key town of Jarabulus from Islamic State (IS) jihadists. / AFP PHOTO / TURKEY'S PRESIDENTIAL PRESS SERVICE / KAYHAN OZER / RESTRICTED TO EDITORIAL USE - MANDATORY CREDIT "AFP PHOTO / TURKEY'S PRESIDENTIAL PRESS SERVICE/ KAYHAN OZER- NO MARKETING NO ADVERTISING CAMPAIGNS - DISTRIBUTED AS A SERVICE TO CLIENTS KAYHAN OZER/AFP/Getty Images

US Vice President Joe Biden (L) gestures next to Turkish Prime Minister Binali Yildirim (R) as they hold a joint press conference following their meeting on August 24, 2016 at the Cankaya Palace in Ankara. US Vice President Joe Biden on August 24, 2016 said Washington had made clear that pro-Kurdish forces in Syria must not to cross west of the Euphrates River, a prospect alarming for Turkey. His comments come after Turkish troops launched an operation inside Syria to cleanse the key town of Jarabulus from Islamic State (IS) jihadists. / AFP PHOTO / ADEM ALTANADEM ALTAN/AFP/Getty Images

Turkish Prime Minister Binali Yildirim (R)and US Vice President Joe Biden (L) hold a joint press conference following their meeting on August 24, 2016 at the Cankaya Palace in Ankara. US Vice President Joe Biden on August 24, 2016 said Washington had made clear that pro-Kurdish forces in Syria must not to cross west of the Euphrates River, a prospect alarming for Turkey. His comments come after Turkish troops launched an operation inside Syria to cleanse the key town of Jarabulus from Islamic State (IS) jihadists. / AFP PHOTO / ADEM ALTANADEM ALTAN/AFP/Getty Images

Turkish Prime Minister Binali Yildiri speaks during a joint press conference with the US Vice President following their meeting on August 24, 2016 at the Cankaya Palace in Ankara. US Vice President Joe Biden on August 24, 2016 said Washington had made clear that pro-Kurdish forces in Syria must not to cross west of the Euphrates River, a prospect alarming for Turkey. His comments come after Turkish troops launched an operation inside Syria to cleanse the key town of Jarabulus from Islamic State (IS) jihadists. / AFP PHOTO / ADEM ALTANADEM ALTAN/AFP/Getty Images

Turkish Prime Minister Binali Yildirim (R) shakes hands with US Vice President Joe Biden (L) at the end of a joint press conference following their meeting on August 24, 2016 at the Cankaya Palace in Ankara. US Vice President Joe Biden on August 24, 2016 said Washington had made clear that pro-Kurdish forces in Syria must not to cross west of the Euphrates River, a prospect alarming for Turkey. His comments come after Turkish troops launched an operation inside Syria to cleanse the key town of Jarabulus from Islamic State (IS) jihadists. / AFP PHOTO / ADEM ALTANADEM ALTAN/AFP/Getty Images

Turkish Prime Minister Binali Yildiri gestures during a joint press conference with the US Vice President following their meeting on August 24, 2016 at the Cankaya Palace in Ankara. US Vice President Joe Biden on August 24, 2016 said Washington had made clear that pro-Kurdish forces in Syria must not to cross west of the Euphrates River, a prospect alarming for Turkey. His comments come after Turkish troops launched an operation inside Syria to cleanse the key town of Jarabulus from Islamic State (IS) jihadists. / AFP PHOTO / ADEM ALTANADEM ALTAN/AFP/Getty Images