The government of Iraqi Kurdistan, the autonomous region in the country’s far-north, is doubling down on the independence referendum it will hold next month in the face of intense lobbying by the Trump administration to delay the vote.

U.S. Defence Secretary Jim Mattis met with Kurdish President Massoud Barzani in the capital, Erbil, on Tuesday, where he renewed Washington’s call for the vote to be postponed to protect Iraq’s stability and ensure full focus on the fight against the Islamic State militant group (ISIS). 

“Our point right now is to stay focused like a laser beam on the defeat of ISIS and to let nothing distract us,” he said before the meeting.

But Kurdish officials have grown increasingly frustrated with Washington’s calls for the Kurds to sideline their political ambitions for nothing in return, particularly after three years of intense cooperation in the battle to liberate ISIS from large tranches of territory in northern Iraq and Syria.

“We can’t cancel it because it would just be a disaster. The president would be paying a big political price for cancelling the vote in exchange for, at this stage, nothing,” a security official in the Kurdistan Regional Government tells Newsweek, speaking on condition of anonymity. 

Mattis’ appeal was only the latest on the part of Washington. Secretary of State Rex Tillerson has made two personal calls to Barzani in recent months to recommend he delay the vote. The chief of the U.S. Central Command, Gen. Joseph L. Votel, visited Iraq and met with Barzani and Kurdish officials last week.

The U.S. government is concerned that splitting up Iraq would not only harm the stability of the country, but fracture the U.S.-led coalition’s campaign against ISIS. Brett McGurk, special presidential envoy for the anti-ISIS campaign, said in remarks made alongside Mattis that a Kurdish vote on splitting away from Iraq would be “potentially catastrophic to the counter-ISIS campaign."

The Kurds are adamant that a referendum will be held, it’s just a matter of when, not if. The bid for independence is so popular among Kurds that it is almost a given that it will pass. A National Democratic Institute poll published in June found that 96 percent of the region’s population supports independence. The only options on the table are to press ahead with the September 25 vote, or a referendum at a later stage when it has greater political support from allies, say officials.

“We’ve had enough of this. The only way we are prepared to postpone the vote is if the Americans give us some sort of assurance for some sort of written agreement on when this vote should be held, and that they will recognise the outcome,” the official says.

But there is an opposition bloc within the Patriotic Union of Kurdistan (PUK), one of two major parties to make up the Kurdistan Regional Government, or KRG, alongside the PUK is the Kurdistan Democratic Party (KDP), which is in favour of the referendum.

Smaller parties, known as Gorran and the Kurdistan Islamic Group (KIG) issued statements opposing the vote, but the PUK and the KDP agreed to the September 25 date for the referendum in June. The Kurds have presented a public front of pressing ahead with the historic referendum ever since.

Barzani himself, at least publicly, has refused to bow to pressure from Washington or other allies. On Tuesday, in remarks delivered to Kurdish representatives, he said that the vote was “the decision of the people” and that he would not accept any verbal promises from Baghdad or the international community.

Ari Mamshae, a staffer in Barzani's presidential team, tells Newsweek that Erbil’s position is clear: “No turning back unless a better alternative is being provided, such as an agreement or a treaty signed by the White House, the U.N., and others. That treaty or agreement will target the same objective, which is independence but perhaps with a little twist. Otherwise, no return.”

So the Kurds need some form of political recognition, and they say any form of economic or political concessions, such as oil-sharing or new positions in the Baghdad government, will be rejected. “That’s not enough. Our presence in Baghdad is largely ceremonial at this stage. There’s a disconnect between,” says the official.

The U.S., Britain, Germany, Turkey and Iran are all opposing the referendum, and McGurk said that “every member of the coalition believes that now is not the time to hold this referendum.” Observers have expressed skepticism that the Kurds can press ahead with the vote without the support of key allies.

“This is the problem with the referendum, that if they go ahead with this, it won’t be recognized by anybody,” says Michael Stephens, research fellow for Middle East Studies at London-based defense think-tank RUSI.

“If they do go ahead with it they will pay a price. The Pentagon phone will be ringing and will not be answered, that’s the way Americans do these things. Barzani will turn up in D.C. and then they say: 'Oh we are so busy, we cannot meet you.'”

With just over one month until the vote, any change of heart would have to take place in the next two weeks. Any reversal within a week of the vote would look “desperate on all sides,” says Stephens.

So there will be much activity in the corridors of Washington, Erbil and Baghdad in the coming days and weeks. But as it stands, the vote is going ahead, and Washington is yet to make its move. 

“We haven’t been offered anything. We haven’t had any assurances from the Americans,” says the Kurdish official. “We need a promise, a real promise.