A Kurdish woman takes part in a gathering Thursday to urge people to vote in the upcoming independence referendum in the town of Bahirka, north of Irbil, the capital of the semiautonomous Kurdish region of northern Iraq. (Safin Hamed/AFP/Getty Images)

Relations between the United States and the Iraqi Kurds, strong allies over decades of intermittent war, are on a collision course that weeks of strenuous U.S. efforts have failed to prevent.

On Monday, Iraq’s Kurdistan region plans to hold an independence vote that the Trump administration says has already undermined the fight against the Islamic State, threatens next spring’s hoped-for reelection of the current Iraqi government and may ultimately destroy the self-sufficient Kurdish region itself.

The rare U.S. inability to sway the Kurds — despite promises of more aid and the quick convening of U.S.- and U.N.-sponsored negotiations with Baghdad over long-standing Kurdish grievances — is a reminder that American influence over even its closest partners in the Middle East has always been limited.

After last-ditch talks in recent days ended in apparent failure, the Kurdistan Regional Government of President Masoud Barzani said it would consider postponing the vote if Washington and Baghdad would guarantee to recognize results of a referendum to be held if one year of negotiations failed. Both capitals consider that proposal unacceptable.

While the upcoming vote is nonbinding, its statement of intent could trigger cataclysmic results, according to U.S. and foreign officials.

“If this referendum is conducted” as scheduled, the State Department said in a stark public statement Wednesday, “it is highly unlikely that there will be negotiations with Baghdad, and the . . . international offer of support for negotiations will be foreclosed.”

“The costs of proceeding” with the vote, it said, “are high,” including jeopardizing Iraqi Kurdistan’s trade relations “and international assistance of all kinds, even though none of Iraq’s partners wish this to be the case.”

“This is simply the reality of this very serious situation,” the statement said.

Some Kurds have called the U.S. position a betrayal. But Kurdish officials sought to tamp down any talk of a rift with Washington.

“It’s not a betrayal,” said Rowsch Shaways, a former deputy prime minister of Iraq and head of the Kurdish negotiations with Baghdad. “Kurdish officials look at the United States as a strategic partner. We will never forget what they have done for us, especially starting from 1991,” when U.S. warplanes began years of air cover to protect the Kurds from Iraqi leader Saddam Hussein.

But still, Shaways said, “it will be very, very difficult for Mr. Barzani, for the political leadership and the Kurdish population itself” to delay the vote “without something tangible” in return.

The potential pain the region could suffer would come not only from the United States but also from Iran and Turkey, the only countries with whom the Kurdistan region shares international borders. Both fear that an Iraqi referendum would spark similar independence moves among their own Kurdish populations. Opposition to the vote is one of the few regional policy issues on which Iran and the United States agree.

In his speech this week to the U.N. General Assembly, Turkish President Recep Tayyip Erdogan called on the government in Irbil, the Iraqi Kurdish capital, to stand down and indirectly threatened to shut down the pipeline through which the Iraqi Kurds export more than half a million barrels of oil a day.

“Ignoring the clear and determined stance of Turkey on this matter,” he said, “may lead to a process that shall deprive the Iraqi Kurdish regional government [of] even the opportunities they currently enjoy.”

The Trump administration has also argued that the referendum would significantly weaken Iraqi Prime Minister Haider al-Abadi, whom it views as a conciliatory leader representing the Kurds’ best partner for negotiations over greater autonomy, said a U.S. official, one of several who spoke on the condition of anonymity about the sensitive diplomatic issue.

Abadi has faced consistent challenges from his predecessor in office, Nouri al-Maliki, and leaders of Iraq’s powerful Shiite militias, many of which are backed by Iran and vehemently oppose Kurdish secession.

“If you want to approach independence in a serious way, this only makes it harder,” said the official, who called the referendum timing “pretty shortsighted.”

U.S. officials are particularly frustrated because they believe Barzani’s determination to carry out the vote is largely an attempt to boost his falling political fortunes among Kurds by playing the nationalist card.

While there is little doubt that the Baghdad government has long dragged its feet on promises to the region, U.S. officials maintain that the Kurds already have much of what they have demanded and that now is not the time to destabilize the country. Although Baghdad has for years failed to pass a hydrocarbons law that would give Iraqi Kurdistan an agreed-on percentage of national oil profits, it has not interfered in Kurdistan’s direct, and technically illegal, export of oil from its northern region through Turkey.

The Kurds, and their peshmerga military forces, are in effective control of Kirkuk, the contested northern city that lies outside the regional government’s boundaries. Arabs and Turkmen populations are substantial in the city, and a referendum to formally claim Kurdish control would require a response — perhaps even a military one — from the Baghdad government and from Turkey.

The referendum also complicated and delayed the operation to retake the Kirkuk province town of Hawijah from the Islamic State.

The town is partly surrounded by Kurdish peshmerga forces, and officials worried that the operation, launched Thursday with an attack by Iraqi security forces, risked sparking ethnic tensions between Kurds and Arabs that could divert attention from the ongoing fight against the militants.

El-Ghobashy reported from Irbil.