The media is abuzz with talk about how the Democratic Union Party (PYD) and its military wing, the People's Protection Units (YPG), which is making substantial gains in Syria against the self-proclaimed Islamic State of Iraq and al-Sham (ISIS) with the assistance of the U.S.-led coalition, aims to establish an autonomous Kurdish state on Turkey's doorstep. The U.S., however, said that it did not support the existence of such a state in northern Syria.The U.S. does not support the establishment of an autonomous Kurdish entity in northern Syria, a special presidential envoy said Tuesday.Gen. John Allen said the U.S does not support the establishment of an autonomous Kurdish entity in Syria and that he believed the Kurds in northern Syria also do not support "a separate governmental entity."In recent weeks, Turkish media reports have claimed that the PYD has tried to alter the population of northern Syria by establishing a Kurdish state that extends from Iraq to the Mediterranean Sea."It is important that a partner that has ultimately been enabled to defeat ISIS does not become an occupying force," Allen told a panel discussion at the Washington-based Center for American Progress, a nonpartisan policy organization.The U.S. does not want the region broken into sectarian or ethnic fragments, he added.Turkey has expressed alarm over a stretching corridor of Kurdish-controlled territory on Turkey's doorstep, a danger that emerged when the PYD and its YPG captured the border town of Tal Abyad from ISIS, combining the cantons controlled by the PYD that run along the Turkish border.The Kurdish advance that was backed by Syrian opposition forces on the ground and U.S.-led airstrikes, handed over the control of ISIS to PYD forces in less than a week, and the capture became a matter of concern for Ankara, which claims there is an intentional demographic change in the domain supported by the U.S.-led coalition. Turkey voiced its reservations that the operation against the strategic Syrian towns, not least Tal Abyad, could be a Kurdish aspiration to force out the ethnic Arabs and Turkmens in the region in order to form a "buffer state" run by the PYD, which Turkey bills as an extension of the PKK in Turkey.Tal Abyad lies between two Kurdish-controlled cantons, Kobani and Jazeera, so its capture is of strategic importance as it opens a supply route between the two spots, triggering Turkish fears that such bridging will ramp up Kurdish power in the region and will ultimately pose a threat to the security of Turkish territory. President Recep Tayyip Erdoğan previously said he was worried that the PYD and the PKK were filling the vacuum left behind after ISIS receded, and that it could "create a structure" near its borders that might threaten the country.Allen also addressed the nuclear deal reached earlier Tuesday between Iran and the world powers, saying that some of the U.S.'s allies are concerned about the agreement."For many of the members of the coalition, Iran has been, is and probably will remain one of the principal sources of threat to their national security," Allen said."I won't speculate on the outcome of the announcement made this morning with respect to whether it will fundamentally change Iran's behavior, but it's of course a very important question for all [coalition members]," he added.