After several days of relative calm, the Russian warplanes resumed heavy bombing of rebel-held eastern Aleppo on Tuesday.
Air strikes mostly hit the Bustan al-Qasr neighborhood, Zakaria Malhifji of the Aleppo-based Fastaqim rebel group said.
"There is renewed bombardment and it is heavy," he said.
The Observatory said at least eight people were killed in Bustan al-Qasr and Fardous neighborhoods.
Moscow and Damascus reduced air raids in the northern city last week. The Syrian army said it was partly to allow civilians to leave opposition-held eastern neighborhoods.
The Syrian government said rebels holed up in Aleppo can leave with their families if they lay down their arms. Insurgents denounced that offer as a deception.
President Bashar al-Assad seeks the complete recapture of Aleppo, Syria's biggest city before the 5-1/2-year war, and which has been divided between government and opposition control for years.
Assad's ally Russia has meanwhile built up its forces in Syria since a brief cease-fire collapsed last month.
Russia's intervention a year ago has helped the government side gain the upper hand against rebels on many frontlines in the Syrian conflict, including Aleppo where the opposition-held sector has been completely encircled for weeks.
Insurgents had advanced elsewhere against government forces and their allies, including in Hama province further south where they captured a series of towns and villages last month. Government forces have regained some of those areas in recent days, however.
In the southern city of Deraa, which is split between government and rebel control, insurgent shelling of a school killed at least five people including children on Tuesday, the Observatory and state media reported. Residents reported the same death toll.
A separate mortar attack hit a government complex in the heart of the city with reports of casualties, a Deraa resident said, adding that mosques were appealing for blood donations.