IRBIL, Iraq — A supposedly secret but locally well-known CIA station on the outskirts of Irbil’s airport is undergoing rapid expansion as the United States considers its options in Iraq, where Sunni militants have seized control in many regions.

Western contractors hired to expand the facility and a local intelligence official confirmed the construction project, which is visible from the main highway linking Erbil to Mosul, the city whose fall June 10 triggered the Islamic State’s sweep through northern and central Iraq. Residents around the airport say they can hear daily what they suspect are U.S. drones taking off and landing at the facility.

Expansion of the facility comes as it seems all but certain that the autonomous Kurdish regional government and the central government in Baghdad, never easy partners, are headed for an irrevocable split — complicating any U.S. military hopes of coordinating the two entities’ efforts against the Islamic State.

The autonomous Kurdistan Regional Government angered Iraqi Prime Minister Nouri al-Maliki early in the crisis, when it sent its peshmerga militia to seize the long-contested city of Kirkuk when Iraqi troops abandoned it. Relations have deteriorated since.

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U.S. officials have known for some time that it was likely that they’d need to coordinate any steps the U.S. takes in Baghdad and in Irbil. The peshmerga has worked closely over the years with the CIA, U.S. Special Forces and the Joint Special Operations Command, the military’s most secretive task force, which has become a bulwark of counterterrorism operations. Peshmerga forces already are staffing checkpoints and bunkers to protect the CIA station, which sits a few hundred yards from the highway.

“Within a week of the fall of Mosul we were being told to double or even triple our capacities,” said one Western logistics contractor who spoke on condition of anonymity because he’d signed nondisclosure agreements with the U.S. government on the matter.

“They needed everything from warehouse space to refrigeration capacity, because they operate under a different logistics command than the normal military or embassy structures,” the contractor said. “The expansion was aggressive and immediate.”

Other contractors who deal extensively with moving heavy equipment through Irbil’s airport, which has supported a rapidly expanding oil- and gas-drilling industry, said they were aware of the expansion.

One British oil executive said he’d detected a “low-key but steady stream of men, equipment and supplies for an obvious expansion of the facility.” The local Kurdish intelligence official described what was taking place as a “long-term relationship with the Americans.”

U.S. Secretary of Defense Chuck Hagel said July 3 that Irbil would host such a center, in addition to one being set up in Baghdad, and suggested it had already begun operating. “We have personnel on the ground in Irbil, where our second joint operations center has achieved initial operating capability,” he said then.

The Kurdish official, who spoke on condition of anonymity, said: “It’s no secret that the American special forces and CIA have a close relationship with the peshmerga.” He added that the facility had operated even “after the Americans were forced out of Iraq by al-Maliki,” a reference to the 2011 U.S. troop withdrawal after the Obama administration and the Iraqi government couldn’t agree on a framework for U.S. forces to remain in the country.

The official refused to directly identify the location of the facility but when he was shown the blurred-out location on an online satellite-mapping service he joked: “The peshmerga do not have the influence to make Google blur an area on these maps. I will leave the rest to your conclusions.”