Hezbollah supporters clash with supporters of the Lebanese Option Party during a protest in front of the Iranian Embassy in Beirut, Lebanon, Sunday, June 9, 2013. A senior Lebanese military official says clashes have erupted outside the Iranian embassy in the capital between protesters opposing Hezbollah's participation in the Syrian war and unidentified Lebanese, killing one demonstrator. Lebanese and Syrian activists chant pro-Syrian revolution slogans during a protest against the participation of Hezbollah in the Syrian war, at Martyrs square in Beirut, Lebanon, Sunday, June 9, 2013. A senior Lebanese military official says clashes have erupted outside the Iranian embassy in the capital between protesters opposing Hezbollah's participation in the Syrian war and unidentified locals, killing one demonstrator. AP Photo/Bilal Hussein A Lebanese activist wearing a shirt with Arabic that reads, "no to Hezbollah weapons in Qusair," flashes the victory sign, during a protest against the participation of Hezbollah in the Syrian war, at Martyrs square in Beirut, Lebanon, Sunday, June 9, 2013. A Syrian family hold Syrian revolution flags during a protest against the participation of Hezbollah's role in the Syrian war, at Martyrs square in Beirut, Lebanon, Sunday, June 9, 2013. BEIRUT (AP) - Men wielding batons and wearing yellow arm bands evoking Lebanon's Hezbollah attacked protesters outside the Iranian Embassy in Beirut Sunday during a rally against the militant group's participation in the Syrian civil war. One protester was killed, a senior Lebanese military official and witnesses said. A military statement said the protesters had just arrived at the embassy area when clashes broke out and a civilian opened fire. The embassy is in a predominantly pro-Hezbollah area. Witnesses saw men wearing yellow armbands - the color of Hezbollah's flag - attacking the protesters with batons. It was unclear if they were affiliated with the militant Shiite group, and the identity of the gunman was unknown, a senior security official said. The official identified the man killed as a 28-year-old member of the small Lebanese Option Party, which had called for the anti-Hezbollah protest. The Syria conflict is increasingly spilling over into Lebanon, home to a fragile mosaic of more than a dozen religious and ethnic groups. Hezbollah's overt participation in the conflict, backing forces of Syria's President Bashar Assad in a successful campaign to drive rebels out of Qusair near the Lebanese border, heightened tensions. The International Committee of the Red Cross said in a statement Sunday that it backed the Lebanese Red Cross in evacuating since Friday 87 Syrians seriously wounded in the fighting in Qusair to hospitals in Lebanon. The leader of Hezbollah, Sheik Hassan Nasrallah, said during the battle for Qusair that he would side with Assad until the rebels are defeated. Assad's Syria is Hezbollah's main ally and supplier of weapons. Gunmen from rival religious sects have gone to Syria to fight on the rebel side. Rebels have threatened to target Hezbollah's bases in Lebanon. Clashes in northern Lebanon between rival Lebanese groups since last month claimed more than 28 lives, and rockets have targeted Hezbollah strongholds. Hezbollah's rivals have increased their criticism, deepening a political stalemate and postponing elections for 17 months. The Lebanese Option Party is headed by a Shiite politician, Ahmad El Assaad, who has long been opposed to Hezbollah. Sunday's clash outside the Iranian Embassy marked rare fighting between two opposing Shiite groups. The official Lebanese National News Agency said the army cordoned off the area of the clashes in southern Beirut. The private Al-Jadeed Lebanese TV said a girl who was protesting was also wounded. The station said the protester who was killed was shot twice in the leg, once in the back, and was hit on the head with a baton. The protest at the embassy coincided with another small rally in downtown Beirut also criticizing Hezbollah's military intervention in Syria's conflict. Dozens of protesters, including many Syrians, converged on Beirut's central Martyrs Square where a large banner read: "Rejecting Hezbollah's fighting in Syria." Those fighting in Syria are not Lebanese. Their culture, their flag, money and weapons are Iranian," said Saleh el-Mashnouk, an ardent critic of Hezbollah. We are here to erase the shame that struck Lebanon because of them. Lebanese protester Samara el-Hariri, 31, said Syria's war is hurting Lebanon's economy and increasing sectarian tension. "My country is stricken," she said. Shiite Iran, Hezbollah's patron, has strongly backed Assad, who belongs to a Shiite offshoot. The fighting in Syria has claimed more than 80,000 lives and displaced several million people. Beside Lebanon, it has also threatened to spill into neighboring countries, like Israel and Turkey. In Syria, fighting between government troops and rebels raged in different provinces, including near the capital, Damascus, and in the northern Aleppo province. Pro-regime media outlets said that after securing control of Qusair, government forces are preparing to move to recapture the contested city of Aleppo next. Activists said there were no signs of a new push on the city or its surrounding areas. The Britain-based Syrian Observatory for Human Rights, which relies on a network of Syrians inside the country for information, said six regime fighters were killed in clashes in Aleppo. The city has been carved up into areas controlled by rebels and the regime, and families have been displaced by shelling. The Observatory also documented a rare case of a public killing of a 15-year-old youth by Islamist rebel fighters in the city of Aleppo. The center said the gunmen detained Mohammed Kattaa late Saturday, accusing him of being an "infidel" for mentioning Islam's Prophet Muhammad in vain. The witnesses told the center the gunmen overheard the teenager arguing with a colleague, telling him that he would not lend him money even if "Muhammad comes back to earth," a common phrase used to describe an impossible task. The men then brought Kattan back to the coffee shop where he works, with his shirt over his face and his back covered in marks from whips, the witnesses told the Observatory. The militants threatened the same punishment for anyone who commits blasphemy, the witnesses said. Then they shot the boy in front of his parents and a crowd before fleeing the scene. It was not clear which rebel group the gunmen belonged to. Rights groups have warned against rising abuses by rebel fighters, including killing of captured regime soldiers or allied fighters. Kattan's case was a rare example of rebels killing a civilian for blasphemy. Associated Press writers Zeina Karam and Yasmine Saker contributed to this report.