Syrian government forces have launched a new offensive against rebels on the outskirts of the city of Aleppo.

The fighting comes after claims by Syrian state television of at least three deaths due to opposition shelling of a district, and just two days after the Syrian army gained full control of Aleppo city.

At least six civilians were also killed on Saturday in air strikes on the rebel-held town of Atareb, west of Aleppo, according to the Syrian Observatory for Human Rights.

The Observatory, a UK-based information office that has been documenting human-rights abuses in Syria, said at least two children were among the dead.

The Observatory could not immediately specify who had carried out the air raids, but Russian and government warplanes typically carry out raids in Aleppo province.

An AFP correspondent in Atareb said military aircraft could be seen circling above the town and a nearby village throughout the day.

Al Jazeera's Hashem Ahelbarra, reporting from Turkey's Gaziantep near the border with Syria, said the new wave of air strikes were concentrated on eastern, southern and northern outskirts of Aleppo, appearing to be aimed at keeping rebel forces away from the recaptured city.

"People are concerned because there are thousands of civilians who are still trapped on the outskirts of Aleppo, particularly those who have been evacuated from eastern Aleppo," he said.

"If the fighting continues, that could further exacerbate the situation."

Russia launched its air war in support of President Bashar al-Assad's forces in September 2015, marking a major turning point in the government's fight against armed opposition groups.

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In another Aleppo-related development, Syrian state TV said an explosion caused by a device left inside a school by rebels rocked the eastern part of the city on Saturday as some residents were returning to their homes.

State news agency SANA said the school had been transformed into "an ammunitions and explosive devices warehouse left behind by terrorist groups in the Sukkari neighbourhood".

Citing a police source, SANA said another 33 people were wounded in the blast, four of them critically, but did not specify whether they were civilians or government troops.

A correspondent for Lebanon's Hezbollah-run Al-Manar TV was reporting live from the area when the blast sounded in the background, sending a huge cloud of dust into the air.

The correspondent later said that at least three people were killed.

The Observatory reported two deaths in the Sukkari warehouse, but said the blast took place as army troops were dismantling explosives.

It said one other person was killed when an explosive device detonated inside a home in the Ansari district.

Elsewhere in Syria, the Damascus water authority said late on Friday that it had resorted to using water reserves to meet the city's demands.

The authority accused rebels who control territory northwest of the Syrian capital of contaminating the water's source, al-Fija spring.

The water authority said it expected the problem to be resolved in a "few days".

Syrian government forces and allied paramilitaries entered eastern Aleppo on Thursday after the last residents and opposition fighters were evacuated from the enclave under a Turkish-Russian deal.

The evacuees left for areas under control of rebels in the western Aleppo countryside and Idlib in northwestern Syria.

The pull-out has given Assad's forces full control over Aleppo, which had been divided between his government and opposition fighters since 2012.

Source: Al Jazeera and news agencies