Warplanes believed to be Russian bombed targets in the southern Syrian province of Deraa for the first time on Wednesday night, a rebel group operating in the area and a group monitoring the conflict said on Thursday.
If confirmed, the air strikes on the Tel al-Harah area would be the furthest south Russian jets have struck in almost a month of air strikes in support of President Bashar al-Assad.
Tel al-Harah is less than 20 km (12 miles) from the Israeli-occupied Golan Heights.
The Syrian air force did not mount nighttime raids, he told Reuters.
The Syrian Observatory for Human Rights, which tracks the war using a network of sources on the ground, also said the jets were believed to be Russian.