Regarding Manbij, Turkish President Recep Tayyip Erdogan has repeatedly declared that his country's ongoing Euphrates Shield operation will target Syrian Kurdish People's Protection Units (YPG) forces there, after they capture the nearby city of al-Bab from Islamic State group militants.
In Sinjar, Erdogan has also threatened to take action against the Kurdistan Workers' Party (PKK) if it retains an armed presence there, alleging that the group is plotting to transform Sinjar into a permanent base, like their Qandil Mountain stronghold in Iraqi Kurdistan.
The fact that Turkey wants both groups - which they view as essentially the same armed group fighting under different flags - to withdraw from these areas isn't the only similarity between the respective situations in Manbij and Sinjar. In both cities, the Kurdish groups have sponsored and trained armed groups from among the indigenous populations, which they want to remain in place even if they do withdraw.
The US, Iraqi government and the autonomous Iraqi Kurdistan Regional Government (KRG) all oppose the PKK's continued presence there. With pressure mounting, the group says they will withdraw, provided the Yezidi Sinjar Protection Units (YBS) militia they armed and trained remain in place to protect the local population.
A guide to the acronyms of the Kurdish region
- PUK - Patriotic Union of Kurdistan. Founded in 1975, the other main political party in the KRG, with its power base concentrated in the city of Sulaimaniah and the contested city of Kirkuk. A social democratic party, it has its own armed Peshmerga forces usually called the 70 Unit.
- PKK - Kurdistan Workers' Party. Armed group founded in 1978 in Turkey; one of its founders and current leader Abdullah Ocalan has been in jail in Turkey since 1999. Waging an armed campaign against the Turkish state since 1984, and outlawed in Turkey as a terrorist group, the PKK has its base in the Qandil Mountains, located in the northeast of Iraq's Kurdistan Regional Government (KRG) territory.
- PYD - Kurdish Democratic Union Party. Founded in 2003 in Syria, it is the most powerful Kurdish political party in Rojava. It is led by two co-chairs, Salih Muslim and Asya Abdullah, and is an ally of the PKK.
- YPG - People's Protection Units (YPG). Founded during the early phases of the Syrian conflict, it is the main armed forces of Rojava, an ally of the PKK and the backbone of the Syrian Democratic Forces (SDF).
"The PKK assists the Yazidis to create a self-defence force and administrative instructions," read a statement released by a PKK-associated political body on January 9. "Once the Yazidis have their own protection force and independent administration, then the PKK's ambitions will be fulfilled in Sinjar.
"The more Yazidis create their force, the less guerrilla force will remain there," the statement added.
The PKK helped the Yazidis defend themselves against the Islamic State group's genocidal assault on their region in August 2014. After a US-backed Kurdish Peshmerga assault forced IS out of the city in November 2015, the PKK and YBS remained. Baghdad subsequently paid some salaries of YBS fighters - to both fight IS and stake some influence in the region, which is disputed between Baghdad and Erbil but has long been under Erbil's defacto control.
With a recent thaw in tense relations between Ankara and Baghdad over Turkey's contentious military presence in Bashiqa, near Mosul, the Iraqi government has taken a firmer line against the PKK's presence in Sinjar.
While the PKK may withdraw its forces from the region in the near future it will likely only do so peacefully if the YBS can retain an armed Yazidi presence in the area.
A similar pattern began emerging in Manbij in mid-2016. Since late 2015, the YPG has fought under the flag of the Syrian Democratic Forces (SDF), which consists of Arabs and other groups fighting IS in Syria. While armed YPG Kurdish fighters still make-up the main component of the SDF, the SDF is promoted as a more inclusive force, capable of capturing cities from IS in Arab-majority parts of Syria without igniting broader Arab-Kurdish hostilities.
In late May 2016, the SDF advanced to the western side of the Euphrates River to capture the Arab city of Manbij. The Americans convinced Turkey to accept this offensive, promising that the SDF assault force would consist primarily of Arab SDF fighters, with only a supporting force of YPG fighters. Ankara reportedly acquiesced under the condition that the YPG contingent withdraw from Manbij once IS was removed.
Manbij fell in mid-August. Turkey, which had previously declared the YPG crossing westward of the Euphrates to constitute a "red-line" to them, launched Operation Euphrates Shield shortly thereafter. The operation has two conspicuous aims, removing IS from that border region and preventing the YPG from linking-up with their remaining isolated Kurdish territory, the northwestern canton of Afrin, and controlling all of Syria's northern border with Turkey in the process.
This is one reason Turkey rushed to capture the border-city of Jarablus from IS on August 24, and why it pushed south against IS in al-Bab - to prevent the SDF from extending further westwards from Manbij, which would bring it closer to Afrin.
The SDF established three military councils to provide security in northwestern Syrian cities captured from IS: the Manbij Military Council, the al-Bab Military Council and the Jarablus Military Council.
In November, the Manbij Military Council claimed it was in full control of Manbij security, and that the YPG forces had withdrawn back to the east bank of the Euphrates, to participate in the ongoing SDF/YPG campaign against IS' Raqqa stronghold.
Turkey remains unconvinced and continues to threaten to take the city.
The al-Bab Military Council was unable to reach al-Bab and capture it before Turkey and Free Syrian Army (FSA) forces launched their ongoing siege on that city.
The first leader of the Jarablus Military Council, Abdulsettar al-Cadiri, was assassinated shortly before the launch of Euphrates Shield. The SDF claims Turkish intelligence was behind his assassination.
The SDF has also vowed to bolster the Manbij Military Council if assaulted by Turkey. Ankara has already targeted their forces in Manbij with air and artillery strikes. No doubt, the PKK would also rush in to bolster the YBS, were Turkey to attack it - likely under the pretext they are a PKK proxy.
Had all these councils been put in place, run by non-Kurdish SDF elements, northwestern Syria would have been under the control of elements allied with the YPG, where they could possibly have been in a position to establish a land-bridge connecting their main territories in northeastern Syria to Afrin.
Continued control over Sinjar would give the PKK a similar advantage. "Sinjar provides a defensive line and also a logistical hub for the area the PKK calls Rojava [Syria Kurdistan]," noted Al-Monitor columnist Mahmut Bozarslan.
"Should the PKK control it, Sinjar would also become a key connection route between its camps in Iraqi Kurdistan and Syria."
It's therefore little wonder that the PKK and YPG are eager to preserve some influence and control over these key areas.
Paul Iddon is a freelance journalist based in Erbil, Iraqi Kurdistan, who writes about Middle East affairs.
Follow him on Twitter: @pauliddon