US-backed Kurdish-Syria force vows to block regime advance

US-backed Syrian fighters say they will not allow regime forces to cross the Euphrates River, in a statement that appears to further entrench Kurdish separatist power in the north of the country.

Syrian Democratic Forces commander Ahmed Abu Khawla said his fighters will respond to "regime provocations", after pro-Assad fighters reportedly fired shots across the Euphrates River. 

"Now we have 3km between us and the eastern riverbank, once our forces reach the area, any shot fired into that area we will consider an attack on the military council," Abu Khawla said.

"We have notified the regime and Russia that we are coming to the Euphrates riverbank, and they can see our forces advancing. We do not allow the regime or its militias to cross to the eastern riverbank."

Despite the warning, pro-regime fighters have advanced deeper into Deir az-Zour in Syria's east where the Kurdish-majority, US-backed force has also launched an offensive.

"The suburbs of this provincial centre (Deir az-Zour) have been liberated. Advance units have successfully crossed the Euphrates and are holding positions on its eastern bank," said Russian Foreign Ministry Spokesperson Maria Zakharova. 

Despite the statement by Russia which is providing air support for the regime, the Syrian Democratic Forces say pro-Assad fighters have not breached the Euphrates yet.

"[This is] mere propaganda... no one has crossed," Abu Khawla told Reuters.

The race to conquer Syria's eastern Deir az-Zour province could lead to a potential clash between the two sides.

Syrian regime media advisor Bouthaina Shaaban has said that pro-Damascus fighters were ready to take on the US-backed force.

"Whether it's the Syrian Democratic Forces, or (the Islamic State group) or any illegitimate foreign force in the country... we will fight and work against them so our land is freed completely from any aggressor," she told Hizballah's al Manar TV.

Syrian Democratic Forces commander Abu Khawla said they too were ready to fight for Deir az-Zour.

"Every village around the eastern riverbank of the Euphrates river until the Iraqi-Syrian border is a goal for our forces," he told Reuters.

"We are moving forcefully and quickly. We do not have a timeline, but we hope soon to free the entire eastern bank."

Abu Khawla added that his forces might eventually take on the Syrian regime - who recently made advances into IS-held areas around Deir az-Zour City - but the fight against jihadi forces remains their priority.

Earlier this month, the Syrian Democratic Forces said they would launch an offensive into IS-held Deir az-Zour, where the regime had made advances.