The Pentagon insists, however, that the SDF is the only force capable of capturing Raqqa, IS’ self-proclaimed capital, and that they need to be properly equipped to do so. The White House is said to be pushing back against the military precisely over concerns about losing access to Incirlik, a sovereign Turkish base of critical importance to the air campaign against the jihadis.

Ankara is likely brandishing the Incirlik card because it is worried that President Barack Obama will sign a bill authorizing the Pentagon to train and equip the SDF before leaving office Jan. 20. The Kurdish and Arab SDF is dominated by the Syrian Kurdish People’s Protection Units (YPG), and Turkey insists that the YPG is no different from the Kurdistan Workers Party (PKK), which is fighting for Kurdish autonomy in Turkey. Thus, arming the YPG, Ankara argues, is the same as arming the PKK . Some US officials privately concur.

Turkish forces and their rebel proxies have been struggling to capture al-Bab for more than a month, but IS fighters have put up fierce resistance. As a result, Turkish casualties are mounting.

US reticence, Cavusoglu charged, was leading the Turkish people to ask, “Why are you letting these people [the Americans] remain in Incirlik?” Defense Minister Fikri Isik echoed his comments, remarking, “The absence of coalition assistance for the al-Bab operation makes one question [their use of] the Incirlik Air Base .”

Turkish Foreign Minister Mevlut Cavusoglu renewed calls today for Washington to sever ties with the Syrian Kurdish-led Syrian Democratic Forces (SDF), the top ally of the US-led coalition against the Islamic State, and to provide air support to Turkish forces fighting to dislodge the jihadists from the Syrian town of al-Bab.

Turkey opened the base to coalition operations on July 22, 2015, after months of wrangling, and in all probability, would wait to gauge President-elect Donald Trump’s position on the YPG before deciding to pull the plug. Incirlik and an early warning radar station in the eastern province of Malatya remain Turkey’s greatest leverage in its perennially fraught ties with the United States. The Malatya facility, part of NATO’s missile defense system in Europe, is also used to spy on Iran.

On a more positive note, Turkish Prime Minister Binali Yildirim is expected to travel to Baghdad in the coming days to hold talks with his Iraqi counterpart, Haider al-Abadi, in a bid to ease tensions stemming from the presence of Turkish troops in northern Iraq. Yildirim will continue on to Erbil, the capital of Iraqi Kurdistan, the day after his Baghdad visit.

The thaw is good news for the Iraqi Kurds and Washington, both of which fret about Turkey following through on its threats to take action against Shiite militias and PKK fighters near Mosul. Iraqi Kurdish officials speaking on strict condition of anonymity told Al-Monitor that Turkey had been on the verge of sending more special forces to the area under the guise of aid workers, but those plans had been frozen largely thanks to US mediation.

Any Turkish intervention in Iraq would likely derail the ongoing campaign to dislodge IS from Mosul. It would also allow Abadi’s opponents, led by his overtly sectarian predecessor, Nouri al-Maliki, to portray the embattled premier as too ineffectual to defend Iraq against foreign incursions.

Speaking to reporters ahead of Yildirim's visit, Abadi confirmed that thorny issues like the PKK would come up during the meeting, which was originally scheduled for Jan. 5, but was postponed a few days. “We are not supporting the PKK, and the Iraqi Constitution absolutely forbids the use [of its territory] for attacks against its neighbors, and we abide by that,” Abadi asserted, responding to claims that his government is arming and funding PKK rebels and their Yazidi affiliates in Sinjar as a counterweight to the Turkish troops based in Bashiqa, north of Mosul.

The dispute between the key allies in the US-led coalition against IS erupted last December, when Turkey deployed several hundred members of its special forces along with 20-odd tanks to Bashiqa, sparking calls from Baghdad for the immediate withdrawal of Turkey’s “occupying force.” Ankara claimed the move was part of its training of Sunni forces to liberate Mosul, but is actually thought to have been spurred by concerns that Shiite militias would seize on the Mosul campaign to engage in revenge killings of Sunni Turkmens who sided with IS when it occupied the nearby town of Tal Afar and ethnically cleansed its Shiite population. The Shiite militias have shown unusual restraint thus far, however, leaving Turkey to focus on its other bugbear, the PKK.

Ankara believes the PKK is looking to use Sinjar as a bridgehead to Syria, where the YPG is growing in strength and numbers by the day. Iraqi Kurdish officials confirm that Ankara will begin training a Syrian Kurdish force to rival the YPG. Linked to the Kurdistan Democratic Party of Syria and based in Iraqi Kurdistan, the force is currently honing its combat skills in the Mosul operation.

Washington has thrown its weight behind Turkish and Iraqi Kurdish calls for the PKK to pull out of Sinjar, partly to diffuse Turkish anger over its alliance with the YPG. US diplomats have been lobbying the different Yazidi groups to unite under the banner of the Iraqi Kurdish peshmerga and sever all ties with the PKK. Their efforts appeared to be paying off when Murat Karayilan, the veteran PKK commander who heads its military wing, was quoted as saying, “We have informed the KRG [Kurdistan Regional Government] that our fighters will soon complete their withdrawal from Sinjar,” although he did not specify when. Iraqi Kurdish officials caution that until the PKK leadership in the Qandil Mountains echoes his words, they do not carry much weight.