Syrian army and Kurdish forces fought separate battles with Islamic State around Hasaka city in northeast Syria overnight as the hardline group tried to capture more areas of the major urban centre near the Iraqi border, a monitor said on Saturday.
Islamic State launched an assault on government-held southern areas of Hasaka earlier this week in violence which the United Nations says is reported to have displaced tens of thousands of civilians.
The Syrian Observatory for Human Rights, which tracks the conflict using sources on the ground, said the Kurdish YPG militia fought with Islamic State fighters on the outskirts of the Ghwyran neighbourhood in Hasaka's southeast.
Hasaka is divided into areas run separately by Syrian President Bashar al-Assad's government and Kurdish authorities and has a mixed population of Arabs, Kurds and Christians.
It is important to all sides fighting in a province that sits between Islamic State-held territory in Syria and Iraq and which reaches north up to the Turkish border.
The YPG says it does not coordinate with the Syrian military, which fought its own battles with Islamic State in the southwestern neighbourhood of al-Nashwa and an area surrounding a security services building in the city, the Observatory said.
Islamic State also attacked the predominantly Kurdish town of Kobani this week, which lies to the northwest of Hasaka on the Turkish border.
The group is reported to have killed at least 145 people in and around Kobani in what the Observatory has described as one of the worst massacres carried out by Islamic State in Syria.