US and Turkey remain divided over Syria path Joe Biden, US vice-president, left, meets Recep Tayyip Erdogan, Turkey's president, in Istanbul on Saturday Joe Biden, the US vice-president, on Sunday rounded off a trip to Turkey in which he sought to bridge the gap with Ankara over the Syrian war but also warned against unchecked executive power - a sensitive topic in a country increasingly accused of authoritarianism. Washington is seeking greater Turkish support for Syrian fighters battling the jihadis of the Islamic State of Iraq and Levant, also known as Isis, even though it remains at odds with Ankara over whether to prioritise the fight against Isis or the ousting of the regime of Bashar al-Assad, Syria's president. In an attempt to overcome the differences with Turkey, US officials suggest Syrian rebels could eventually set up "safe zones" in Syria - a measure Ankara has pushed for Washington and its allies to establish themselves. Under the US proposal, such zones, which would be close to the border, would not be backed by a formal no fly zone - a step requiring a large-scale military operation to eliminate regime air defences - but could be supported by US air power. The battle for Kobani, a Syrian Kurdish town where the US is carrying out air strikes in support of fighters battling Isis, could serve as a template. Officials said the discussions, which involved a four-hour meeting between Mr Biden and Turkey's president Recep Tayyip Erdogan on Saturday, were detailed and would be followed by further consultations. But differences between the two sides remain substantial. While the US has a medium term goal of clearing Isis from the Syrian border with Turkey, Ankara insists that any strategy that does not involve ejecting Mr Assad is incoherent. "If we just deal with the symptoms, but not the illness, things will continue like this," said a Turkish official. Isis will go and another terrorist organisation will come up. The US also wants to use its air base in Incirlik, southern Turkey, in the fight against Isis, particularly for potential search and rescue missions, where the shorter flying time would give it an advantage. The two sides have also yet to finalise a deal for Ankara to train the rebels from the Free Syrian Army, amid a general recognition that plans to train some 5,000 rebels a year are not enough to meet their goals. Mr Biden's visit was all the more sensitive because of a diplomatic imbroglio last month caused by comments in which he accused Ankara of having let jihadi fighters cross over into Syria. Mr Erdogan demanded and secured an apology for those remarks. But Barack Obama, US president, and his administration have also grown increasingly frustrated with Mr Erdogan's alleged authoritarian tendencies over the past 18 months. During that time, the Turkish leader has cracked down on mass demonstrations, derailed a corruption investigation he depicted as a coup attempt and sought to ban Twitter and YouTube. "Our founders concluded that a concentration of powers was the most corrosive thing that could happen to any system," Mr Biden told a non-governmental group in Istanbul on Saturday. Though his comments described the emergence of the US constitutional order and he said he did not intend to proselytise, they alluded to US concerns about Turkey, with the vice-president also warning that "the best way to preserve freedom is not to have too much power concentrated in any branch of government."