Syrian fighters supported by Turkish air power on Thursday clashed with the mostly Kurdish Syrian Democratic Forces militia at a new front on the Euphrates.
The violence marks an expansion of a conflict n eastern Syria in which hundreds have been killed since the fall of Bashar Al Assad on December 8.
A spill over from the Syrian civil war, the Arab-Kurdish conflict, has indirectly pitted Turkey and the US against each other, with Washington the only major power left backing Syria's armed Kurds. But the US, diplomats say, has been encouraging the SDF to talk to the new rulers in Damascus, led by Hayat Tahrir Al Sham (HTS), a group formerly linked with Al Qaeda.
A Telegram group affiliated with the attacking forces said fighting broke out in Deir Hafer, an area near an artificial lake, formerly called Assad lake, in Aleppo province.
The forces comprise the Syrian National Army (SNA) and Arab militiamen who defected from the SDF after the fall of the Assad regime. The SNA is a Turkish proxy set up by Ankara in northern Syria in 2015. A video circulated by SNA supporters on social media purportedly showed Turkish drone attacks on Kurdish positions in Deir Hafer overnight.
An SDF statement said "international powers should play their role" by "putting pressure on the Turkish occupation [forces] to stop their attacks".
The group remains committed to "participating in the political process to build a new Syria", it added.
In the past three weeks, fighting in the east has been mainly around the Tishreen Dam in the north, where the SDF on Wednesday said 20 civilians had been killed by Turkish drone attacks on the area. There was no independent confirmation of the death toll.
The tribal east, especially in the Euphrates Valley, is the source of most of Syria's oil and gas. Output was 200,000 barrels a day before 2011 but has fallen by 75 per cent since. The area also contains the bulk of the US military presence in Syria.
At least several hundred people have been killed in the east since the fall of the Assad regime. The death toll was made up of SDF and anti-SDF fighters, as well civilians killed in a crackdown by the SDF on an Arab uprising last month.
In Damascus, the Syrian News Agency reported that Defence Minister Murhaf Abu Qasra on Thursday met representatives of Arab tribes, many of whom are from the east, in a show of support for the new HTS-dominated order.
Mr Abu Qasra said talks were continuing with the SDF on bringing "state institutions" into the east, as well as control of energy resources and the border with Iraq.
The Kurdish "file" is being dealt with deftly but "we are ready for all probabilities", said Mr Aby Qasra, who is also an HTS commander..
His forces, considered the most lethal faction in the country along with the SDF, have not participated in any significant way in the latest clashes in the east, but they took control over several areas in the eastern Raqqa and Deir Ezzor governorates after the SDF pulled out in recent weeks.
A western diplomat said US officials were engaged with Turkish authorities in talks in Ankara about the future of east Syria, with the US pressuring the SDF to "put forth a wide vision of the Kurdish role in a future Syria".
The SDF has been the ground component in the US fight in Syria against ISIS, which still maintains a presence in the east. An estimated 10,000 to 12,000 people who the SDF says are linked to ISIS are imprisoned in the east.
At the World Economic Forum in Davos, meanwhile, Syria's Foreign Minister Asaad Al Shibani revealed the country's HTS-led interim government has been in contact with the new Trump administration in the US, without revealing details. Talking to Damascus would help the US achieve security and stability in the region, he said.
