At an emergency meeting on Sunday, Arab foreign ministers urged warring Lebanese factions to cease fighting, and decided to send a mission including Arab League General Secretary Amr Moussa to broker a settlement between the government and the Hezbollah-led opposition.
The Arab League issued a statement critical of the Shiite militant Hezbollah.
"The ministers reject the principle of resorting to armed violence to achieve political goals," it said.
According to media reports, the Syrian-backed Islamist group Hezbollah took control of the Muslim half of Beirut on Friday after three days of fighting with pro-government militias.
At least 20 people have reportedly been killed and over 50 wounded in the worst internal clashes since the 1975-90 civil war.