A young Lebanese man demonstrating against the involvement of Hezbollah and Iran in neighbouring Syria's war has been fatally shot outside the Iranian embassy in Beirut.

Al Jazeera correspondent Mohamed Vall, reporting from the Lebanese capital, said the shooting incident happened at about lunchtime on Sunday near the Iranian embassy in Bir Hassan, which is in an area where support for Shia group Hezbollah is strong.

The protesters were mainly demonstrating against the increased logistical and military support for the Syrian government by Hezbollah and Iran.

It was not clear who started the firing. Vall said that a small group of young men began to protest but were then attacked by another small group. Several protesters were hit in the ensuing gunfight.

"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.

Ahmad Asaad, a Shia politician who is anti-Hezbollah and belongs to the March 14 movement, said the victim's name was Hashem al-Salman, and that he was killed intentionally.

"He was a student leader in our party, and he and I were close," said Assaad.

"Hashem was Shia. His execution proves that Hezbollah's problem is not with other sects in Lebanon, but with anyone who dares to oppose them," Assaad told the AFP news agency.

An army statement confirmed the protester's death.

"This afternoon, as members of a political movement arrived in the Bir Hassan neighbourhood.There was a clash during which a man opened fire with a revolver," the statement said. "A civilian was critically injured and has since died."

Anti-Hezbollah rally

Al Jazeera's Nour Samaha, reporting from Beirut, said that those protesting against Iran and Hezbollah belonged to Ahmad Asaad's party.

The Lebanese army was reported to be in control of the area around the embassy, with barricades set up on the road.

In central Beirut, about 50 people also gathered to denounce Hezbollah's involvement in the Syrian conflict, Samaha said.

The demonstration was called for by Saleh Mashnouq, anti-Hezbollah activist and son of a prominent Sunni politician, Nouhad Mashnouq.

"The protest ended without incident. The army and Internal Security Forces reopened the roads that were previously blocked, and took down barricades and barbed wire that had been erected," Samaha reported.

Vall said Sunday's clash in Bir Hassan was indicative of the rising tensions in Lebanon over the deteriorating situation in Syria, with Hezbollah fighters helping the forces of President Bashar al-Assad.

Syrian rebels have fired rockets into Lebanon, while supporters inside the country have clashed with Hezbollah.