Syrian troops have clashed with rebels on the southern outskirts of Damascus and in the northern city of Aleppo, activists said, in a flare-up that is part of a government push to advance and retake opposition-held areas.
In the suburbs of Damascus, Tuesday’s fighting centred around the town of Hejeira, one of a patchwork of sprawling neighbourhoods and towns south of the Syrian capital that have been opposition strongholds for the past year.
Activists said President Bashar al-Assad's troops were backed by Shia fighters from Iraq and the Lebanese armed group Hezbollah.
Emboldened Assad troops have in recent weeks made advances on the battlefield, taking back at least four strongholds in the northern province of Aleppo and south of Damascus.
This week, government forces recaptured the town of Sbeineh, adjacent to Hejeira.
In Aleppo city, Syria's former commercial hub, government forces were bent on recapturing districts from opposition brigades, activists said on Tuesday.
They said that rebels saw the threat of Assad wresting back Aleppo as so grave that self-declared Islamist brigades and al-Qaeda-affiliates declared on Monday an emergency and summoned all fighters to head to the fronts.
The joint declaration said government forces - backed by Shia Hezbollah fighters, Iranian Revolutionary Guards and the Iraqi Abu al-Fadl Abbas armed group - had launched "a fierce offensive to reoccupy" Aleppo.
The fighting in Syria has become increasingly sectarian, with mainly Sunni rebels fighting against loyalists of Assad, who belongs to the Alawite sect, an offshoot of Shia Islam.
Dozens of combatants have been killed in the last few days in embattled northern and eastern areas of Aleppo.
Aleppo has been divided roughly in half by the warring parties for much of the conflict but the government is determined to reassert total control to solidify a foothold in the north where rebel supplies stream in from Turkey.
After 32 months of the conflict, which started after Assad's forces fired on anti-regime demonstrators and escalated into a full-blown civil war, the fighting has settled into a stalemate in which scores of people are killed every day.
More than 120,000 people have been killed, according to the UN and opposition activists, and more than two million people have fled to neighbouring countries.