Airstrikes killed at least 30 civilians in the oil-rich province of Deir al-Zour in eastern Syria on Friday, a monitor group reported.
The Syrian Observatory for Human Rights said it's not clear whether the airstrikes were carried out by Syrians or Russians, adding that children and women were among those killed when the warplanes struck areas in the town of Tabyet Jazeera in the eastern countryside of Deir al-Zour.
The UK-based watchdog group said it was the second airstrike that has targeted Deir al-Zour on Friday, bringing the overall death toll to 40.
A day earlier, the Observatory said intense battles have been raging in Deir al-Zour since mid-January between Syrian government forces and the Islamic State (IS) group.
The battles are focused in the northwestern part of Deir al-Zour, where the IS group unleashed a wide-scale offensive on Jan.16 against Syrian army positions, managing to make some gains, according to the Observatory.
The London-based watchdog group said days of battles were coupled with daily airstrikes by government forces. It added that over 200 government soldiers and 110 IS militants have been killed.
The Observatory, which relies on a network of activists on ground, said the IS group was making use of the tough weather conditions to make progress against the Syrian military positions. It added that the terror group succeeded in capturing parts of the Ayash arm depots and the al-Saeka military camp during its offensive.
The progress has enabled the IS to open a supply line between its controlled areas in the western countryside of Deir al-Zour and the newly fallen areas in the northwestern part of the city.
Following its offensive in Deir al-Zour, the IS group stormed the town of Bughailiyeh, killing over 200 civilians and tossing their bodies in the Euphrates river, according to the Observatory.
It added that 400 civilians were snatched by the ultra-radical group in the town, 270 of whom, either minors or elderly, were later released as the rest will be interrogated on charges of dealing with the Syrian army.
The IS group has been suffering defeats recently in Syria during battles with Syrian ground troops who are backed by intense Russian air cover.
The group will feverishly strengthen its positions in Deir al-Zour, due to its strategic location near the Iraqi borders and its oil fields. The province is the richest among Syrian provinces in term of oil, one of the main lifelines of the IS group.