At least nine civilians were killed on Tuesday as Russia resumed its air strikes against opposition fighters in Syria's northwestern Idlib province.
Rami Abdel Rahman of the Syrian Observatory for Human Rights said the warplanes resumed their strikes after a 22-day pause.
The West has warned against the repercussions of a military operation on the territory.
The Observatory said at least nine civilians, including five children from the same family, were killed in the raids, while 10 people were wounded.
The strikes targeted 24 areas and "came a day after opposition units in Idlib hit regime positions in neighboring Latakia province, which killed three pro-regime fighters," Abdel Rahman told AFP.
The head of the regime, Bashar al-Assad, has sworn to recapture every inch of Syria and has made big gains against the opposition since Russia joined his war effort in 2015.
Last week, a source close to Damascus said the regime was preparing a phased offensive to recover Idlib province, but Turkey, whose army has a string of observation posts around the edge of the area, has warned against such an assault.
Russian air raids ceased in and around Idlib on August 15, but pro-Syrian regime forces have maintained an aerial bombardment and shelling against opposition fighters there, the Syrian Observatory for Human Rights said.
An opposition source and the Observatory both said the air strikes were in the countryside near Jisr al-Shughour on the western edge of the opposition's northwestern territory.
Russian, Turkish and Iranian leaders are due to meet on Sept. 7 in Iran and are expected to discuss the situation in northwestern Syria.
US President Donald Trump on Monday warned the Syrian regime against launching an attack on Idlib, saying the offensive could trigger a "human tragedy."
Assad “must not recklessly attack Idlib Province. The Russians and Iranians would be making a grave humanitarian mistake to take part in this potential human tragedy," Trump tweeted.
In a speech to EU ambassadors, the EU foreign policy chief, Federica Mogherini, also warned that an offensive would bring destructive results on the Syrian people who have been already suffering greatly due to the civil war.
She added that the EU should exert strong efforts to prevent the offensive.
