Midnight explosions rocked Syria's northern province of al-Raqqa, the de facto capital of the Islamic State (IS) group, a monitor group reported.
The explosions were believed to be airstrikes targeting areas in al-Raqqa and its countryside, Xinhua cited the Syrian Observatory for Human Rights as saying on Sunday.
The Observatory said the late night airstrikes created unknown losses.
Earlier in the day, the UK-based watchdog group said over 40 people, including children, were killed by airstrikes against al-Raqqa.
The city has become the target of the US-led anti-terror coalition and the Russian airstrikes. It is the main stronghold of the IS in Syria.