However Israel, which has traditionally enjoyed relatively close relations with the Kurds, has officially endorsed the vote.
The US will not be able to sustain its support for an independent Kurdish state without the support of some of its regional allies, especially Turkey.
Turkey is flexing its military muscle on the northern Iraqi border in a show of force against next week's planned vote on Kurdish independence.
Turkey stationed troops in Bashiqa near Mosul, ignoring protests from Iraqi Prime Minister Haider al-Abadi, ahead of the military campaign to drive Islamic State out of the northern Iraqi city.
On Tuesday, Iraq's central government authorized the prime minister to "take all measures" to preserve the country's unity.
Turkey has now found "common ground" with the Assad regime in countering the YPG, said Gonul Tol, director of the Middle East Institute's Center for Turkish Studies.
The proposed referendum has provoked deeply mixed reactions among Iraqi Kurds.
With the 5 million Kurds who are eligible to vote largely united by dreams of self-determination, the outcome appears in little doubt.
Turkey, for years the KRG's main link to the outside world, has built strong trade ties with the semi-autonomous region which exports hundreds of thousands of barrels of oil per day through Turkey to global markets.
However, with the vote due to be held on September the 25th and many are anxious that tensions may lead to clashes.
Foreign ministers of Iran, Iraq and Turkey, namely Mohammad Javad Zarif, Ibrahim al-Ja'afari and Mevlut Cavusoglu made the remarks in a joint statement issued Thursday following a meeting on the sidelines of the UN General Assembly session in NY. The Iraqi government will try to prevent this from happening if need be by resorting to military force. Home to a larger Kurdish population spread over valued arable land and strategic territory, Turkey faces more severe ramifications within its borders than Iran does in the event that Iraqi Kurdistan declares independence.
Iraq's top court has temporarily suspended the vote, and the country's parliament has also voted to reject it. "I don't think they're going to say, sure, take the oilfields and Kirkuk and go your way", Thomas told a security forum. And he has made clear he is not going to run for the president again, already his term expired.
Kurds in north Syria, like those in Iraq, have capitalized on the turmoil in both countries to consolidate a degree of autonomy. The first big obstacle comes here because none of the 5 permanent members - China, France, Russia, the United Kingdom and the U.S. - must veto the application.