Relations between the People's Protection Units (YPG) and the Free Syrian Army (FSA) are unclear and varied among the different FSA factions. Both are opposed to the Islamic State of Iraq and the Levant. However, several clashes between the two have taken place. Under pressure from the United States (who has assisted both), some FSA groups coordinate with the YPG to battle ISIL under the name of the Syrian Democratic Forces, although some other FSA groups remained in conflict with the YPG and the SDF, including FSA groups in the SDF. After the fall of the Assad regime, most FSA factions were incorporated into the newly formed Syrian Ministry of Defense, with only a few FSA factions remaining within the SDF.
Timeline
2012–13
Early clashes The earliest incident of YPG–FSA fighting happened between 29 June and 2 July 2012. FSA groups and the PYD clashed in the town of Afrin, during which two rebel fighters and one ex-PYD member were killed."The impending Syrian-Kurdish conflict"
On 25 October, some 200 rebels moved into the district of Ashrafiyeh in the YPG-controlled area of Sheikh Maqsud of Aleppo city. It was the first time that government or rebel forces moved in a substantial way into the Kurdish areas. Previously the area had been regarded as neutral with Kurdish militia clashing with both rebel and army units. The rebel unit responsible is allegedly the Liwa al-Tawhid brigade who reportedly told the locals "We are here to spend Eid with you." Ashrafiyeh is important as a part of the city heights and controls routes between the north and south of Aleppo.Syrian rebels take Aleppo Kurdish area Previous rebel attempts to move into the district had been repelled.
Rebel activists have claimed that Kurdish forces had either reached agreement with rebels to allow their rapid advance or assisted the rebels by simply leaving their checkpoints overnight. One rebel spokesman has even gone as far as to indicate that Kurdish forces may join the Free Syrian Army.
On 26 October, rebels clashed with Kurdish militias that tried to stop them entering the Sheikh Maqsud neighbourhood. 19 rebels and 3–5 Kurdish fighters were killed. One Kurdish leader said that they had "a gentlemen's agreement" with the rebels that they would not enter Kurdish areas and that the rebels had violated it when they entered Ashrafiyeh. According to another report, by activists who organised a Kurdish protest at a PYD militant checkpoint between the Kurdish areas of Ashrafiyeh and al-Sheikh Maqsoud, rebel fighters opened fire on the protesters, leaving eight dead and five wounded. The Kurds warned that this may lead to clashes between Arab and Kurdish fighters in the area. Overall, the PYD stated that 10 Kurds were killed during the clashes, including the three fighters. SOHR put the Kurdish toll at 11, for a total of 30 dead, when including the 19 rebels. 200 people were kidnapped or captured as a result of the fighting. The PYD captured 20 rebel fighters, while the rebels detained 180 Kurds, civilians and fighters,"Fears of new front as Syria rebels clash with Kurds" , Khaleej Times, October 2012. 120 of them near the town of Hayyan. SOHR said that the PYD was still in control of the Ashrafiyeh neighbourhood. A PYD statement published after the fighting blamed both the Syrian army and the FSA for the violence. "We have chosen to remain neutral, and we will not take sides in a war that will only bring suffering and destruction to our country," the statement said. The rebels said that the clashes started after their forces attacked a security compound in Ashrafieh, which was defended by both PKK fighters and government troops.
On 28 October, near the Kurdish village of Yazi Bah, close to the Turkish border in the Aleppo countryside, rebel forces reportedly tried to storm the town of Qastal Jindo (al-Kastal). During the fighting that followed between the PYD and the rebels, 4–5 rebel fighters were killed. Among the dead was also Abou Ibrahim, the leader of the rebel Northern Storm Brigade. He previously claimed responsibility for the kidnapping of 11 Lebanese Shiite pilgrims. The next day, SOHR reported that a Kurd, taken prisoner by the rebels near Hayan, was tortured to death.
On 30 October, the third consecutive day of clashes at al-Kastal, the town was shelled with mortars from the rebel stronghold of Azaz. Sporadic gunfire also occurred near the village. Meanwhile, in a new round of clashes in the Kurdish areas of Aleppo city, rebels opened fire on Kurdish protesters killing three of them. The day after, PYD fighters ambushed rebels near the rebel-held Turkish border crossing of Bab al-Salameh, killing one fighter and wounding two. On 2 November, the rebels reportedly executed Shaha Ali Abdu, a Kurdish PYD militia leader, who they previously captured in Aleppo city while she was on a mission to return the bodies of rebel fighters that were killed during the clashes between the FSA and the Kurdish militia. Reports of Shaha Ali Abdu's execution were later found to be untrue as she turned up unharmed in the town of Afrin 9 days later. The next day, a government airstrike on Ras al Ain killed 7 rebels.
YPG and FSA truce signed On 5 November, both YPG and FSA signed a truce, promising release of detainees and closer cooperation in fight against the Assad government.
Battle of Ras al-Ayn
On 8 November 2012, the FSA attacked Syrian army positions in town of Ras al-Ayn () and later released video showed FSA fighters in control of the town. Al-Kurdiya News correspondent on the ground also said that local Kurds aided the FSA in the attack. According to Turkish journalist Mehmet Aksakal two Turks have been injured in the border town of Ceylanpınar. He also suggested that clashes may be result of growing dissatisfaction between KNC (ENKS) and PYD. However, another Kurdish activist claimed that even though PYD had their armed wing in the city, it was controlled fully by the government and PYD did not participate in clashes. Around 10 rebels and 20 Syrian soldiers were killed in the fighting, while about 8000 residents fled to Ceylanpınar as fighting raged.Thousands flee heavy clashes on Syria border
On 10 November, YPG militiamen aided by local Kurds stormed the last government security and administrative stations in the towns of Al-Darbasiyah () and Tel Tamer. This attack was prompted by violence in Ras al-Ain where the FSA stormed the town because of the presence of government security units. It also left only 2 major towns in hands of government in Al-Hasakah Governorate – Al-Hasakah and Qamishli.Kurds seize two towns in Syria's northeast, watchdog says The following day, an airstrike conducted on Ras al-Ayn by the Syrian Air Force killed at least 16 individuals in the town.
On 13 November, YPG militia forced out remaining security units from the town of Al-Malikiyah (), in order to prevent FSA from having an excuse to launch an attack like in Ras al-Ayn. On 14 November, FSA fighters took control of an army post near Ras Al Ain, reportedly killing 18 soldiers based there. On 15 November, FSA announced that they had taken full control of Ras Al Ain capturing or killing the last remaining Syrian Army soldiers stationed there. There were also no government airstrikes in the town for the first time in the past 3 days as Government forces appeared to have given up in trying to retake the city.
On 19 November, the FSA launched an assault on a PYD checkpoint in Ras al-Ayn that initially left six rebels dead. The rebels also assassinated Abed Khalil, the president of the local Kurdish PYD council, when a sniper shot him dead. The next day it was reported by SOHR that the death toll in the rebel-PYD fighting in the town had reached 34. 29 of the dead were members of the rebel Islamist Al-Nusra Front and the Gharba al-Sham battalion. The other five included four Kurdish fighters and the Kurdish official. The four Kurdish fighters were reportedly executed after being captured by the rebels. The opposition activist group the LCC put the number of dead at 46: 25 Kurdish and 20 FSA fighters and the official.Ivan Watson and Ammar Cheikh Omar, "Dozens dead after clashes in Syrian border town", CNN, 20 November 2012 35 Kurds and 11 FSA fighters were captured by both sides.
As a result of the fighting, there has been a buildup in the number of forces deployed by both sides in Ras al-Ayn. By 22 November, Kurdish forces had strengthened their numbers to around 400 militiamen, who faced 200 fighters from the Al-Nusra Front and 100 fighters from Ghuraba al-Sham, supported by three captured Syrian Army tanks.
On 19 November, members of the al-Nusra Front and Ghuraba al-Sham opened fire on a YPG checkpoint, sparking clashes that killed dozens of people, including at three rebel leaders. A Kurdish activist stated that the presence of hostile Islamist fighters had alienated Kurdish locals. Both the Kurdish National Council and top FSA commander General Riad al-Asaad condemned the clashes, with the KNC calling the presence of rebel fighters in the town "pointless and unjustifiable", and al-Asaad attributing the violence to "some groups trying to exploit the situation in order to blow up relations between Kurds and Arabs" while expressly denying any FSA affiliation with Ghuraba al-Sham.
On 22 November, SOHR reported that eight members of the al-Nusra Front and one PYD fighter were killed in fighting for Ras al-Ayn. The fighting had claimed an estimated 54 lives to date. The next day, however, a tenuous two-day ceasefire was announced between Kurdish fighters and Islamist militants of the al-Nusra Front and Ghuraba a- Sham in order to determine terms of a possible permanent agreement between the two sides. Prior to this announcement, the PYD claimed that its forces had killed 25 rebels, wounded 20 more, and destroyed three vehicles.
On 3 December, air raids conducted by the Syrian Air Force on a police station and old post office in the Mahatta neighbourhood killed twelve and injured dozens more. Among the dead were six Kurds, three of them children. Ambulances from Turkey took at least 21 of the wounded to a hospital in the predominantly Kurdish town of Ceylanpınar across the border. Turkey scrambled a number of F-16 fighter jets based at Diyarbakir in response to the strikes.
On 22 January 2013, at least 56 people were killed in a week of fighting in northeast Syria between anti-government rebels as hostilities re-opened in Ras al-Ayn.
On 17 February, an agreement was reached between the Kurdish Supreme Committee and FSA groups in Ras al-Ayn. The terms of agreement include the withdrawal of all foreign fighters from Ras al-Ayn, joint checkpoints between the YPG and the FSA, the establishment of a joint city council in Ras al-Ayn, the creation of a local police force, and cooperation between the two groups to fight the Syrian government.
Battle of Tal Tamr On 14 February 2013, FSA-affiliated fighters tried unsuccessfully to storm a cattle farm in Tal Tamr, sparking a firefight with YPG units in which several of the attackers were killed.
2014–16
Siege of Kobanî (September 2014 – March 2015)