The U.S. does not recognize the Kurdish Regional Government's (KRG) "unilateral referendum" on independence from Iraq, the State Department said Friday.
"The vote and the results lack legitimacy and we continue to support a united, federal, democratic and prosperous Iraq," Secretary of State Rex Tillerson said in a statement.
Tillerson said the U.S. remains concerned about the fallout from the poll in which Kurds overwhelmingly voted to leave Iraq, emphasizing that before the vote Washington worked with Erbil and Baghdad "to pursue a more productive framework and to promote stability and prosperity for the people of the Kurdistan region.
"These aspirations, ultimately, cannot be advanced through unilateral measures such as this referendum," he said.
The poll has been denounced by Iraq and its neighbors, who view it as illegitimate, and Baghdad has moved to ban international flights into the KRG and close foreign missions in the Kurdish region.
Earlier Friday, Talar Faiq, director of Erbil's international airport, announced all international flights into the Kurdish region would be suspended as of 6 p.m. local time (2100GMT).
Exceptions would be made for military, diplomatic and UN-affiliated flights.
U.S.-led coalition forces frequently use the Erbil airport for military purposes, while the UN uses both the Erbil and Sulaymaniyah airports to dispatch humanitarian aid to war-torn areas of Iraq.
In addressing the ongoing diplomatic row, Tillerson urged the parties to halt "vocal recriminations and threats of reciprocal actions", and pursue dialogue.
"We urge Iraqi Kurdish authorities to respect the constitutionally-mandated role of the central government and we call upon the central government to reject threats or even allusion to possible use of force," he said.
"The fight against ISIS/ Daesh is not over, and extremist groups are seeking to exploit instability and discord. We urge our Iraqi partners to remain focused on defeating ISIS/Daesh," he added.
According to figures released by the KRG, almost 93 percent of voters cast ballots Monday in favor of independence from Baghdad.
