The situation in Syria continues to confuse
The US has said fighting between Turkey and some opposition groups in northern Syria is "unacceptable and a source of deep concern".
Brett McGurk, special presidential envoy for the coalition to counter Islamic State, said: "We want to make clear that we find these clashes - in areas where ISIL is not located - unacceptable and a source of deep concern."
"We call on all armed actors to stand down...the US is actively engaged to facilitate such deconfliction and unity of focus on ISIL, which remains a lethal and common threat."
His words, quoting a briefing by the Department of Defense, come after Turkey sent its troops into Syria, alongside Syrian rebel fighters with the stated aim of stopping terrorism from both Islamic State (IS) and Kurdish militants.
With Kurdish fighters quickly capturing land along Syria's border with Turkey, however, the Turkish incursion was also to prevent any further Kurdish gains.
DOD: We want to make clear that we find these clashes -- in areas where #ISIL is not located -- unacceptable and a source of deep concern.— Brett McGurk (@brett_mcgurk) August 29, 2016
Along with the US, Turkey is an important member of NATO but the Kurdish fighters it is attacking are a major part of the US fight against IS led by the Syrian Democratic Forces (SDF).
Turkey sees the Kurdish YPG militia as an extension of the illegal Kurdistan Workers' Party (PKK).
Sky's Foreign Affairs Editor Sam Kiley said the US had shown "considerable unease - I would say considerable anger - at the focus of the Turkish operations, which have been entirely against the Americans' close allies in the Kurdish-led militia".
DOD: Accordingly, we call on all armed actors to stand down and take appropriate measures to deconflict & open channels of communication.— Brett McGurk (@brett_mcgurk) August 29, 2016