The Syrian air force continued an escalation in bombing on Monday, assisting an Islamic State offensive on rebel-held areas in Aleppo Province in northern Syria. The Local Coordination Committees reported confirmation of 83 deaths across the country, with 35 of them in Aleppo Province and 25 in Idlib Province.Significantly, most of the Aleppo deaths were from regime strikes on Mare’ and Tel Rifaat, where rebels are trying to hold back the Islamic State offensive that surged over the weekend. Mare’ has been at the frontline for months, with the militants seeking to regain positions that they lost in early 2014 when battles erupted with rebel factions.Video from Mare’ showed rescuers trying to save people, including a child, under the rubble of destroyed buildings.

The Syrian military is fighting the Islamic State in other areas of the country, having lost Palmyra in central Syria to the militants two weeks ago. In eastern Syria, the two sides are fighting in Deir Ez Zor and Hasakah Provinces.

As recently as Saturday, the Assad air force was bombing Islamic State-held areas in Aleppo Province, killing at least 51 people in al-Bab. However, as soon as the Islamic State challenged rebels along a 25-km front north and northeast of Aleppo city — pulling back from their threat to regime positions to the east — the Syrian aerial assault focused on rebel territory.

Activists are also claiming that Syrian forces in regime enclaves in Nubl and Zahraa, north of Aleppo city, are setting fires to hinder the move of rebel reinforcements.

State news agency SANA, in contrast to its reports of “stepped-up military operations leaving dozens of terrorists killed”, makes no reference to the military in Aleppo Province.

On Monday, the US Embassy in Syria, taking a much sterner line than officials in Washington, claimed a de facto regime-Islamic State alliance: