Two rockets have hit a district in southern Beirut, controlled by Hezbollah.
The missiles, Soviet-made Grad rockets, hit buildings in the al-Shayyah area and injured three people.
Syrian rebels have vowed to attack Hezbollah after their leader Hassan Nasrallah promised to support Syrian President Bashar al-Assad until the rebels were defeated.
"We used to say before, 'We are coming Bashar'," Col Abdul-Jabbar al-Aqidi was quoted as saying. "Now we say, 'We are coming Bashar and we are coming Hassan Nasrallah'.
Dozens of Hezbollah fighters are thought to have died in Syria while fighting against rebels alongside the Syrian army.