The Syrian army says its forces have captured a string of villages in the east of the country from US-backed rebels.

Syrian state television said on Sunday that government troops had gained control of several settlements east of the Euphrates River near the border with Iraq from the Kurdish-led Syrian Democratic Forces (SDF).

The US-supported militia, mainly comprised of the Kurdish YPG, had taken much of the territory in Deir el-Zour province as part of a major campaign last year that drove Isis forces out of eastern Syria.

Earlier on Sunday, the SDF said they were engaged in heavy clashes with Syrian army troops on the outskirts of the village of Janin near the Euphrates.

British-based war monitor the Syrian Observatory for Human Rights, said the offensive had left six SDF fighters dead and 22 wounded. Adding government forces had also suffered casualties.

The SDF accused the Syrian authorities of seeking to disrupt preparations by the US-led coalition to resume an imminent offensive against Isis in several pockets of territory they still control along the Euphrates.

"We affirm that we are determined to eradicate terrorism from its roots and to assert our right to self-defence," SDF spokesman Kino Gabriel said in a statement.

"We consider this aggression by regime forces to be a support for terrorism and falls within the attempts to impede the war on terrorism."

The Russian-backed Syrian army led by president Bashar al-Assad has rarely clashed with SDF forces in its campaign against Isis, generally keeping clear of areas east of the Euphrates.

Government troops have instead focussed on regaining territory from militants west of the river.

There have been elaborate "deconfliction lines" separating the US-led coalition forces present on the eastern side of the river from the Russian and Iranian backed forces on the western side to prevent clashes, according to US army officials.

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Earlier on Sunday, the SDF said they were engaged in heavy clashes with Syrian army troops on the outskirts of the village of Janin near the Euphrates.

They accused the Syrian authorities of seeking to disrupt preparations by the US-led coalition to resume an imminent offensive against Islamic State in several pockets of territory they still control along the river.

In February, US air strikes killed and wounded hundreds of pro-Assad troops in western Syria, including Russian paramilitary contractors, who were advancing near the city Deir al-Zor.

The government forces had been closing in on one of the largest gas fields currently in the hands of US.-backed groups.