The Syrian army backed by the Lebanese armed group Hezbollah launched an assult on the city of Zabadani, near Damascus, in a fresh push to seize the last rebel stronghold along Lebanon’s border.

Syrian TV reported on Saturday that President Bashar al-Assad's troops closed in on the rebels "on several fronts" and had inflicted heavy casualties on the fighters.

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Hezbollah TV station earlier said the Syrian army and its air force had begun a major aerial bombing campaign against rebel outposts along the Lebanese border. It showed footage of plumes of smoke hanging over Zabadani.

Helicopters belonginig to the Syrian army asking residents to stay away from "sites, arm depots and supply routes used by terrorists."

On Friday, rebels captured several military posts on the outskirts of Zabadani belonging to the army and Hezbollah, as part of a pre-emptive attack they named "the revolutionary volcano".

Opposition fighters have been in control of the city, located 50km northwest of Damascus, since 2012, despite several attempts by Assad's troops to retake it. The city has witnessed near daily shelling since then.

Rebel gains in Aleppo

Elsewhere in Syria, rebels have seized a strategic military centre in the government-held western part of Aleppo city, as fierce battles raged between opposition and government forces, a monitor said on Saturday.

The Syrian Observatory for Human Rights said a coalition of rebel groups had taken the Scientific Research Centre, which was being used as a military barracks.

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Observatory director Rami Abdel Rahman said the fall of the centre opened potential lines of attack against several other government-held neighbourhoods.

Aleppo, once Syria's economic powerhouse, has been divided between the government in the west and rebels in the east since shortly after fighting there began in mid-2012.

Meanwhile, in Idlib province, at least 25 fighters from the al-Qaeda-affiliated Nusra Front were killed in a bombing inside the al-Salem mosque in the city of Ariha. The attack was claimed by the Islamic State in Iraq and the Levant (ISIL).

A suicide bomber detonated himself inside the mosque after the evening prayer, killing al-Nusra commanders and civilians, while injuring dozens of others, the activist group added.

Ariha was one of the last government strongholds in Idlib until it was captured in May by a rebel coalition named the Jaish al-Fateh army, which include Nusra Front.

On Friday, ISIL suffered a blow in the northern city of Raqqa after the Kurdish People's Protection Units, or YPG inched closer to the city and closed the main route the self-declared group allegedly uses to supply Raqqa from Turkey.

Infographic: Syria map update [Al Jazeera]

Source: Al Jazeera and agencies