Lebanese security forces inspect the damage after attack on Beirut May 26 Two rockets exploded into the Hezbollah heartland of south Beirut on Sunday as fighters from the Lebanese Shiite group battled alongside regime forces against rebels in a key town in neighbouring Syria. The attack came as Syria's fractured opposition began an unscheduled fourth day of meetings on a peace conference proposal and after Hezbollah pledged "victory" in Syria over the rebels.
Its chief Hassan Nasrallah said it was in the militant anti-Israel group's own interest to defend President Bashar al-Assad's regime.
"I say to all the honourable people, to the mujahedeen, to the heroes: I have always promised you a victory and now I pledge to you a new one" in Syria, he said in a speech for the 13th anniversary of Israel's withdrawal from Lebanon.
Hours after he spoke, two Grad rockets hit the Al-Shayyah area of south Beirut, wounding four Syrian workers at a car dealership and badly damaging an apartment.
It was the first time the Lebanese capital's Shiite southern suburbs have been targeted during the more than two-year-old conflict in Syria.
 A security source said the four wounded in the showroom were all Syrian workers. An AFP photographer said the second rocket hit an apartment block and caused widespread damage but no casualties.
"This is an act of sabotage," Interior Minister Marwan Charbel said at the scene.
The security source said the rockets were fired from Aitat in the Mount Lebanon area some 13 kilometres (8 miles) southeast of where they hit.
"The army is on the way to this area to investigate."
The fighting in Syria has already spilled over into Lebanon's second city, the northern port of Tripoli, where 30 people have been killed in a week of clashes between pro-Assad Alawites and pro-rebel Sunni Muslims.
The intervention of hundreds of Hezbollah fighters has given Assad the upper hand in Qusayr, a strategic central town in Syria across the border with Lebanon, that had been in rebel hands.
Syrian forces launched an assault on Qusayr last Sunday but are still being fiercely resisted, as the town provides an important rebel supply line for arms and volunteers from Lebanon.
Nasrallah's victory pledge followed rare criticism of Hezbollah by Lebanese President Michel Sleiman, who cautioned it against its intervention in Syria.
 The Syrian Observatory for Human Rights said at least 27 rebels and three civilians, including a child, were killed in Qusayr on Saturday.
Qusayr is a key prize for Assad because of its strategic location between Damascus and the mainly Alawite Mediterranean coast.
The main opposition Syrian National Coalition in a statement on Sunday urged Hezbollah fighters in Syria to defect.
It was meeting in Istanbul again to try to overcome deep divisions over Russian and US proposals for a peace conference.
The opposition's long-standing position is that, after more than two years of devastating conflict which has killed more than 94,000 people, it will not negotiate until Assad agrees to leave.
Delegates said efforts to reach an agreed position on the conference were being delayed by pressure from some of the opposition's Gulf Arab backers for an overhaul of its membership.
"You have Saudi Arabia and the United Arab Emirates pushing to include up to 30 new members in the National Coalition," a Coalition member said on condition of anonymity.
"Their goal is to downsize the Muslim Brotherhood's influence over the group," he added.
The National Coalition is currently dominated by the Syrian National Council, in which the main political bloc is the Muslim Brotherhood.
The Coalition, wrong-footed by Moscow's announcement that regime representatives had agreed to attend next month's planned peace conference, urged Damascus to give concrete evidence of its readiness for a transition of power.
The United States and Russia, which support opposite sides in Syria's conflict, are pushing for the conference. On Monday US Secretary of State John Kerry will meet Russian counterpart Sergei Lavrov in Paris to step up efforts to organise it.
Israel, meanwhile, accused Syrian forces of trying to provoke conflict as the two sides rowed over responsibility for a border clash.
Tensions around the Golan Heights ceasefire zone have escalated since Syrian forces fired across the UN-patrolled ceasefire line and hit an Israeli military vehicle on Tuesday.
"This week's events are part of a disturbing pattern of events intended to spark provocation with Israel," Israel's UN ambassador Ron Prosor wrote in a letter to the UN Security Council on Saturday.