Syrian regime forces enter IS-held Mayadeen

Syrian regime forces on Friday entered the eastern town of Mayadeen, one of the Islamic State group's last bastions in war-torn Syria.

The government troops advanced on the ground backed by Russian military aircraft, which have already claimed the lives of a number of civilians around the extremist-held town.

"With support from Russian aviation, regime forces entered Mayadeen and took control of several buildings in the west of the town," Rami Abdel Rahman, head of the Britain-based Syrian Observatory for Human Rights, told AFP.

Situated in the province of Deir az-Zour, Mayadeen is viewed as the IS group's "security and military capital" in Syria. Its fall to the regime of President Bashar al-Assad would deal "a severe blow" to the militants, according to a Syrian military source.

Successive defeats for IS in Iraq and Syria have made Mayadeen and nearby Albu Kamal refuges for fleeing IS fighters. Many of the fighters have fled from the battle for Raqqa in the north, where US-backed Kurdish and Arab forces are fighting to take the city.

IS remains in control of half of Deir az-Zour province, despite advances by Assad's forces and a separate offensive against the militants by the Kurdish-Arab alliance.

The Observatory said the target of the regime advance was to recapture the Al-Omar oilfield held by IS to the northeast of Mayadeen that was destroyed in US-led coalition air strikes in 2015.

The extremists had been drawing oil sale revenues from the field of between $1.7 million and $5.1 million a month, according to the coalition.

Advances against IS in Deir az-Zour have come with a heavy civilian death toll from Russian and US-led coalition air raids.

The Observatory said Russian air strikes on Thursday night killed 14 people, including three children who were fleeing across the Euphrates on rafts near Mayadeen.

On Wednesday, another Russian air strike killed 38 civilians trying to flee the fighting in Deir az-Zour province, according to the Observatory.

The US-led coalition, meanwhile, killed at least 18 civilians in a strike on Raqqa on Tuesday.

The Red Cross said on Thursday that Syria is experiencing its worst levels of violence since the battle for east Aleppo late last year.

"For the past two weeks, we have seen an increasingly worrying spike in military operations that correlates with high levels of civilian casualties," said Marianne Gasser, the head of the International Committee of the Red Cross delegation in Syria.