At least 18 civilians have been killed in the ISIS-capital of Raqqa, Syria, according to local activists.

The monitoring group Syrian Observatory for Human Rights (SOHR) said dozens more were injured in raids on Tuesday night. The British-based group said it was not able to verify who had carried out the strikes although another group said Russian warplanes were to blame, according to the BBC.

Six children were among the dead, the SOHR said as it warned the number was likely to rise due to dozens of injured civilians being in a critical condition. Another activist group, Raqqa is Being Slaughtered Silently (RBSS), listed the names of the 18 dead and said 28 others were wounded.

The strikes came after Russian-backed government forces were dealt a blow by ISIS in fighting around the town of Tabqa, 40km west of Raqqa. Two days of intense clashes forced the Assad-army back in a setback to the campaign to recapture the Syrian city. The ISIS controlled Amaq news agency released a video that purportedly showed jihadis in control of the Thawra oil fields after Assad's army had recaptured them on Sunday.

ISIS militants face a two-pronged attack in Raqqa and neighbouring Aleppo from both the Russian-backed Syrian forces and the US-backed Kurdish and Arab fighters.

Meanwhile Assad has asked his electricity minister Emad Khamis to form a new government, according to state media agency SANA. No details were given on why Khamis would replace Wael al-Halaki as prime minister, or whether Halaki would be included in the new administration or had left government. Halaki himself replaced a prime minister who defected to the opposition.