Former Lebanese Prime Minister Saad Hariri, who heads the largest bloc in parliament, has formally endorsed a leading Christian politician and strong ally of the Hezbollah group to become the next president.

Hariri's backing of Christian leader Michel Aoun Thursday is likely to open the road to the presidential palace for the 81-year-old politician, increasing chances that the majority of the 128-member parliament would vote for him.

Lebanon has been without a head of state since the term of President Michel Suleiman ended in May 2014.

Hariri's move is likely to anger many Sunnis in the country who are opposed to Hezbollah and Aoun and don't want an ally of Syria to become head of state. Hariri is also facing stiff resistance from parliament's powerful speaker, Nabih Berri.