Massud Barzani, leader of the autonomous region, earlier told parliament to make preparations for a "referendum on the right of self-determination."

But the White House, which has been working behind the scenes to try to convince Iraq's Sunni, Shiite and Kurdish leaders to form a unified government in Baghdad, gave the idea a cool reception.

"The fact is that we continue to believe that Iraq is stronger if it is united," said White House spokesman Josh Earnest.

"That is why the United States continues to support an Iraq that is democratic, pluralistic and unified and we are going to continue to urge all parties in Iraq to continue working together toward that objective," Earnest said.