Beirut - A mortar shell struck an election gathering in southern Syria for President Bashar Assad, killing a number of people, state media and opposition activists reported on Friday.
Assad, rarely seen in public since the start of Syria's 3-year-old conflict, has not been seen campaigning since he announced his candidacy last month and was not at the gathering in the southern city of Daraa, where the uprising against his rule began.
More than 160 000 people have been killed in the fighting as the revolt morphed into civil war that's also sent millions fleeing for their lives and turned once-prosperous cities into rubble-strewn warzones.
The state-run Sana news agency said the mortar strike late on Thursday killed an unspecific number of people. The Britain-based Syrian Observatory for Human Rights, which relies on activists on the ground for its reports, said the shelling targeted an "electoral tent" where Assad's supporters had gathered and killed 21 people, including 11 civilians.
There was no immediate claim of responsibility for the attack. Rebels trying to overthrow Assad frequently fire mortar shells into Syria's major cities, including the capital, Damascus, from opposition-held suburbs.
The attack underscores concerns that rebels will step up attacks against government strongholds in the run-up to the election to disrupt the voting.
In Lebanon, Interior Minister Nouhad Machnouk has warned Syrian refugees against holding rallies and gatherings ahead of the vote.
More than a million Syrians have sought shelter in Lebanon, straining the country's resources and threatening to re-ignite the Arab nation's own explosive sectarian mix. Fighting between Lebanese factions supporting opposing sides in Syria's conflict has frequently broken up in Lebanon.
In a statement on Thursday, Machnouk asked the refugees "not to hold any political gatherings and not to hold public meetings with political dimensions that could in any way affect the security and stability of Lebanon".
He also called on the Lebanese security force to show "no leniency and deal firmly with any act or activity that could destabilise the internal security".
In Syria, public gatherings by Assad's supporters are being held, often in tents, in some government-controlled parts of the country ahead of 3 June presidential election.
Assad is widely expected to win a third, seven-year mandate in the vote criticised by the West and opposition groups as a sham.
Assad's family has ruled Syria for more than 40 years. Though this year's vote will be the first time the family has faced challengers as opposed to a yes-or-no vote on their rule, a recently passed election law makes it impossible for those leading the revolt against Assad to compete.
Assad was last seen in public on 20 April when Syrian state television broadcast images of him visiting the ancient Christian village of Maaloula north of Damascus. Government forces recently recaptured the town, part of a series of major advances ahead of the vote.
On Thursday, Syrian tanks backed by massive air power rolled into the grounds of a sprawling prison in the northern city of Aleppo, breaking a yearlong rebel siege and allowing Assad's forces to close in on a nearby rebel command centre.
Aleppo is Syria's largest city and has been carved up into government- and rebel-held areas since the opposition fighters launched an offensive in the north in mid-2012.