BEIRUT — An offensive by Syrian insurgents aimed at the government-held part of the northern city of Aleppo has killed at least 74 civilians, including 25 children, an opposition monitoring group said Saturday.

The insurgents launched the assault eight days ago, hoping to break a monthslong government siege on the rebel-held eastern part of the city, which has been subjected to months of devastating Syrian and Russian airstrikes. The insurgents have seized a district on Aleppo's edge and a nearby village.

The Syrian military said the first three days of the rebel offensive killed more than 80 people. It was not immediately possible to reconcile the different figures.

Rights groups and the United Nations have sharply criticized the rebels over the shelling of western Aleppo districts, which has killed a number of civilians. Such criticism had mainly been focused on the government and its allies, accusing them of indiscriminate shelling and airstrikes on rebel-held areas.

Moscow declared a halt to airstrikes on eastern Aleppo on Oct. 18, but Syrian and Russian warplanes have continued to strike around the city's edges and in the surrounding province. The strikes, which have hit a school and several medical facilities, have killed more than 400 civilians in less than a month and wounded more than 2,000 people. The Britain-based Syrian Observatory for Human Rights recorded three civilian deaths in rebel-held Aleppo districts in the past week.

On Friday, a renewed 10-hour Russian offer of a moratorium on airstrikes expired. None of the estimated 275,000 residents of eastern Aleppo departed during the unilateral cease-fire, as they had been urged to do by Russia and the Syrian government.

Russian officials had not said what would happen when the deadline expired. But the arrival of a Russian aircraft carrier into the Mediterranean and its heading to the Syrian coast suggested Moscow may intend to escalate its operations.

The chairman of the Russian parliament's defense committee, Vladimir Shamanov, told state TV Rossiya 1 last week that the carrier's arrival in Syria is part of a rotation schedule and also “a show of the flag.”

On Saturday, Syria's pro-government Sama TV said another Russian ship has arrived in the Mediterranean to “reinforce the other military ships already present at the Syrian coast.” There was no immediate word from the Russian Defense Ministry.

By late afternoon Saturday, there were no reports of airstrikes in the city of Aleppo, but Syrian activists reported air raids in the surrounding province.

Footage from the activist-run Thiqa News Agency appeared to show missiles targeting the town of Darat Izza in northwestern Aleppo province.

A team of first responders known as the Syrian Civil Defense, or White Helmets, said at least three people were killed in the airstrikes and 15 others were wounded.

There has been an intense aerial bombing campaign in the western Aleppo countryside and nearby Idlib province in recent days.

Rebels said it appeared to be an attempt to sever their supply lines.