American-educated billionaire Najib Mikati has been appointed prime minister-designate of Lebanon, despite an outcry by supporters of his predecessor, Saad Hariri.
Mr Mikati is backed by the Shi'ite Islamist group Hezbollah and its allies, the BBC reports.
The move came despite demonstrations by thousands of supporters of outgoing Prime Minister Saad Hariri in the city of Tripoli.
Smaller protests were also reported in the capital, Beirut, and elsewhere. Mr Hariri has condemned acts of violence.
After his appointment, Mr Mikati said he hoped the new government would serve all of Lebanon, and protect its unity and sovereignty.
Hezbollah's leader, Sheikh Hassan Nasrallah, urged him to form a coalition including all political and sectarian factions.