An global delegation, including the US, Britain and United Nations envoys, met with Kurdish President Masoud Barzani and presented the alternative path for the controversial independence referendum.
Kurdish lawmakers convened parliament in Irbil for the first time in two years to pass the measure, with 65 out of 68 parliamentarians in the 111-seat body present voting in favor.
The statement warned the independence vote could distract from efforts to defeat the Islamic State terror group (IS).
"The United States does not support the Kudistan Regional Government's intention to hold a referendum later this month", the White House said in a statement.
"Holding the referendum in disputed areas is particularly provocative and destabilizing", it added.
In June, Kurdish leaders announced a plan to hold a vote on Kurdistan's independence and scheduled it for September 25.
Analysts say the referendum plan, which has stirred Arab-Kurdish ethnic tensions, could mark the end of an era of cooperation during which Baghdad and Erbil battled IS after its seizure of swathes of northern and western Iraq in the summer of 2014.
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Masoud Barzani, the Kurdish Regional Government (KRG) president, said Thursday he could consider an offer to delay the independence referendum.
Under this plan, a well-placed source told AFP, the global community will oversee negotiations on revenue sharing in Iraq's oil budget and payment for Kurdish militia fighters.
Opposition parties Goran and Jamaa Islamiya earlier said they would boycott the session.
United States officials, however, remain insistent: "There is no chance that this referendum, which will be held on September 25, will be given global legitimacy ..."
Turkey and Iran are against the referendum over concerns it could have a knock-on effect on their Kurdish minorities. It is also created to strengthen Barzani's position as a Kurdish nationalist leader.
Baghdad recognises Kurdish autonomy in some areas of Iraq but the precise boundary of the Kurds' self-ruled region and the rest of the country is disputed.