A young Lebanese man demonstrating against Hezbollah's participation in Syria's war was shot and fatally wounded Sunday, in the first such incident in Beirut, a security official told AFP.
Shots were fired in front of the Iranian embassy on the outskirts of the capital, where opponents of the Iran-backed Shiite movement Hezbollah were demonstrating against its involvement in the two-year-old conflict in neighbouring Syria.
"The victim was shot in the back while he took part in an anti-Hezbollah demonstration in front of the Iranian embassy," the official said on condition of anonymity.
The official said he did not know who had fired the shots.
The army confirmed a man had died from wounds caused by gunfire at the protest.
"This afternoon, as members of a political movement arrived in the Bir Hassan neighbourhood (where the Iranian embassy is located), there was a clash during which a man opened fire with a revolver," an army statement said.
"A civilian was critically injured and has since died."
Tehran is a key supporter of Syria's President Bashar al-Assad, whose regime is also backed by Hezbollah.
An AFP photographer at the scene said the young anti-Hezbollah protesters were attacked by party supporters wielding sticks, who also assaulted journalists in the area.
The clash ended minutes later when the army intervened. The photographer saw at least one person suffering from wounds, his face covered in blood.
Tensions in fragile Lebanon have soared since Hezbollah announced it was fighting alongside regime forces against rebels in Syria's Qusayr, which the government captured last Wednesday after a massive offensive.
The now devastated Syrian town of Qusayr is just 10 kilometres (six miles) from the border with Lebanon.
In central Beirut, around 100 people also gathered to condemn Hezbollah's involvement in the Syrian conflict.
Security forces were deployed in force around the city centre to prevent trouble.
"Hezbollah needs to get out of Syria. They are doing what no other Lebanese armed movement has ever done before, and that is to participate in a war in another country," protest organiser Charles Jabbour told AFP.
"Lebanon has never been so fragile. They are transferring the Syrian conflict into Lebanon. The Lebanese army should deploy on the border to stop Hezbollah from entering Syria."
The protesters chanted slogans denouncing Assad and in support of the rebels fighting the regime.
Syria's conflict has created deep divisions among Lebanese, pitting supporters of Hezbollah against the Sunni-led March 14 bloc, which supports the anti-Assad revolt.
The Lebanese army has warned against "plots" to drag the country into the war.