HASAKA - The Kurdish YPG militia launched a major assault on Monday to seize the last government-controlled parts of the northeastern Syrian city of Hasaka after calling on pro-government militias to surrender, Kurdish forces and residents said.They said Kurdish forces began the offensive after midnight to take the southeastern district of Nashwa, close to where a security compound is located near the governor's office close to the heart of the city.The powerful YPG militia had earlier captured Ghwairan, the only major Arab neighborhood still in government hands.The fighting this week in Hasaka, which is divided into zones of Kurdish and Syrian government control, marks the most violent confrontation between the Kurdish YPG militia and Damascus in more than five years of civil war.The Syrian army deployed warplanes against the main armed Kurdish group for the first time during the war last week, prompting a US-led coalition to scramble aircraft to protect American special operations ground forces.The YPG is at the heart of a US-led campaign against the Islamic State militant group in Syria and controls swaths of the north, where Kurdish groups associated with the militia have set up their own government since the Syrian war began in 2011.Syrian state media accused the YPG-affiliated security force known as the Asayish of violating a ceasefire and said its members had torched government buildings in Hasaka.It accused the Asayish of igniting the violence through escalating "provocations", including the bombing of army positions in Hasaka, and said the Asayish aimed to take control of the city."WE WILL NOT RETREAT"The YPG denied it had entered into a truce. It distributed leaflets and made loudspeaker calls across the city asking for army personnel and pro-government militias to hand over their weapons or face death."To all the elements of the regime and its militias who are besieged in the city you are targeted by our units," leaflets distributed by the YPG said."This battle is decided and we will not retreat ... We call on you to give up your weapons or count yourselves dead."The YPG, known as the People's Protection Units and which has ties to the Kurdistan Workers Party, appeared intent on leaving a nominal Syrian government presence confined to within a security zone in the heart of the city, where several key government buildings are located, Kurdish sources said.The complete loss of Hasaka would be a big blow to President Bashar al-Assad's government and would also dent efforts by Moscow, which had sought through a major military intervention last year to help Damascus regain lost territory and prevent new rebel gains.Kurdish forces have expanded their control of the city despite the bombing of several locations by Syrian jets.Thousands of civilians in the ethnically mixed city, including members of the Christian community, have fled to villages in the countryside as the fighting intensified, residents said.The confrontation appears to have undone tacit understandings between the YPG and the Syrian army that had kept the city relatively calm.Many critics and residents say the YPG was handed weapons and territory by the Syrian army at the start of the conflict as Assad sought to focus on crushing the mainly Sunni Arab rebels who sought to topple him.Hasaka's governor told state media after the flare-up of violence the military had armed the YPG with weapons and tanks to fight jihadist elements but had not expected them to turn against them.Hasaka's population, swelled by displaced Syrians fleeing areas that fell under Islamic State control, is broadly divided along ethnic lines, with Kurds mainly in the city's eastern neighborhoods and Arabs in the southern parts.