Syrian Kurdish militia have seized several positions from government forces in the divided city of Hasaka, a Kurdish official said on Friday, expanding their control in one of the heaviest clashes yet between Kurdish groups and the government. The fighting this week led to the first use of Syrian air force jets against Kurdish groups. The government has not commented on the fighting. Democratic Union Party (PYD)-linked the Kurdish People's Protection Unit (YPG) militia holds wide areas of northern Syria, where its political allies have set up an autonomous government since Syria's civil war began in 2011. The government still has a foothold in the cities of Hasaka and Qamishli. The Kurdish forces, which already hold most of Hasaka city, had taken government-held buildings including an economics college, said Naser Haj Mansour, a Kurdish official in the YPG- affiliated Syria Democratic Forces alliance. The Syrian Observatory for Human Rights, which reports on the war using an activist network, said Kurdish forces had gained ground in the southern part of the city.

The YPG and Syrian government have mostly avoided confrontation during the multi-sided war, which turned Syria into a patchwork of areas held by the state and an array of armed factions. Kurdish groups are working to develop their autonomy in northern Syria into a federal system of government, a plan opposed by Bashar Assad. Rami Abdulrahman, Observatory director, said the fighting began after pro-government militiamen detained Kurdish youths, a step that had followed advances by Kurdish security forces towards government-held areas. It is the second major eruption of fighting between the YPG and Syrian government fighters this year. In April, the sides fought several days of lethal battles in Qamishli, north of Hasaka city at the Turkish border. It is also mostly YPG-held. The Observatory says at least 13 people, including children and women, have been killed as a result of shelling by the army on Kurdish-controlled areas of Hasaka. It said many civilians were fleeing areas affected by the fighting to safety, and hospitals in Kurdish areas of the city did not have enough blood and medicines to treat the wounded.

PYD has been accused of making ethnic cleansing in the territories, it has captured. Therefore, the group has been suffering from lack of support from local Arabs as wells as other Kurdish groups. The tension between the rival Kurdish parties have been rising recently as PYD seeks to be the only ruler in Syria's north. Moreover, PYD's relations are also broken with Kurdish Regional Government (KRG). Speaking to Anadolu Agency, Khalid Ali, a member of the Syrian Kurdish Democratic Party, said Syrian Kurdish fighters, Syrian peshmerga, were considered a "threat" to the PYD. After the eruption in 2011 of the conflict in Syria between the Assad regime and armed opposition groups, many Syrian Kurds fled to the northern Iraqi provinces of Erbil and Dohuk, both of which are part of the semi-autonomous Kurdish region.