Moscow — Some 120 Daesh (the so-called IS) fighters and 60 foreign mercenaries were killed in a series of Russian air strikes in Syria over the past 24 hours, the defense ministry in Moscow said on Saturday.

"A command post of the terrorists and up to 80 (IS) fighters including nine natives of the Northern Caucasus were destroyed in the area of Mayadeen," the ministry said, adding some 40 IS fighters were killed around the town of Albu Kamal.

As a result of an air strike more than 60 foreign mercenaries from the former Soviet Union, Tunisia, and Egypt were killed south of Deir Ezzor.

The ministry said the "large numbers of foreign mercenaries" were coming into the Syrian border town of Albu Kamal from Iraq.

Mayadeen is one of the Daesh group's last bastions in Syria.

Meanwhile, Syrian regime forces Friday broke into the eastern town of Mayadeen, one of the Daesh group's last bastions in Syria, backed by Russian air raids taking a deadly toll on civilians.

Mayadeen in the oil-rich eastern province of Deir Ezzor is seen as the militant group's "security and military capital" in Syria, and its loss would deal "a severe blow" to the militants, according to a Syrian military source.

Over the course of months of successive defeats, Mayadeen and nearby Albu Kamal on the Iraqi border have taken in IS fighters fleeing the battle to the north for Raqa city in the face of an offensive launched by US-backed Kurdish and Arab forces.

"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.

Mayadeen, which the militants have controlled since 2014, sits on the western bank of the Euphrates River, between provincial capital Deir Ezzor, where the militants still hold several districts, and the border with Iraq.

IS remains in control of half of Deir Ezzor province, despite advances by President Bashar Al-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 militants had been drawing oil sale revenues from the field of between $1.7 million and $5.1 million a month, according to the coalition.

On another front, regime forces said Friday they had ended their military operations in the east of central province of Homs, after "eliminating the last groups" of IS fighters from an area of 1,800 square km (700 square miles), the official Sana news agency reported.

The advances against IS in Deir Ezzor have cost a heavy civilian death toll from Russian and coalition air raids. — Agencies