The world wants to wash its hands of the people who have escaped the Islamic State.
Turkey conveyed it "cannot tolerate the PKK establishing some kind of a state structure along our border in Syria.”
The Turkish forces are part of a coalition that includes Syrian rebels and American aircraft aimed at pushing ISIS from the Syrian border town of Jarablus.
The attack, which consisted of a motorcycle and truck bombing, took place in the Kurdish city of Qamishli near the Turkish border early Wednesday morning.
Rebels have said in the past that their attacks on the Kurdish-held Sheikh Massoud neighborhood were in response to attempts by Kurdish militiamen to cut the only road into rebel-held Aleppo.
Islamic State fighters withdrew from frontlines with Syrian rebel forces north of Aleppo on Wednesday as the rebels mounted a counter attack against the jihadist group.
"It's significant in that it's their last remaining funnel" to Europe, a US military official said, adding that the offensive will be supported by a small number of US special operations forces.
Friday's advance was the biggest by Islamic State in Aleppo province for two years, bringing the jihadists to within 3 miles of Azaz, a town near the border with Turkey through which anti-government insurgents have been supplied.
The American troops were photographed and videotaped on the frontlines of a Kurdish-led offensive against the Islamic State in Syria.