The balance of power in Lebanon shifted towards Syria and Iran on Tuesday when a Hezbollah-backed politician was named prime minister, ousting a Western-allied bloc that has headed governments for nearly six years.

Sunni Muslims loyal to outgoing premier Saad Hariri staged a "day of rage," burning tyres and blocking roads in protest at the appointment of Sunni billionaire Najib Mikati, a centrist lawmaker with ties to both Saudi Arabia and Syria.

"My hand is extended to all factions to take part and end division...through dialogue," Mikati said after his nomination.

Hezbollah and its allies quit Hariri's unity government on January 12, bringing it down after the failure of a Syrian-Saudi effort to bridge a rift over a UN-backed tribunal set up to try the killers of Hariri's father, statesman Rafik al-Hariri.

Fury in Lebanon over Hariri's assassination in 2005, along with U.S., French and Saudi pressure, had forced Syria to pull out its troops and relax its domination of its neighbor.

Almost six years later, it is Syria's Lebanese allies, with the pro-Iranian armed Shi'ite group Hezbollah at the forefront, who have regained the initiative from their pro-Western rivals.

And they have done it legally and constitutionally, winning support for Mikati from 68 of parliament's 128 members after Druze leader Walid Jumblatt, once a Hariri ally, switched sides.

But in Lebanon's tortuous politics, parliamentary arithmetic may be less important than securing sectarian consensus.

"If most of the Sunni community doesn't accept Mikati's designation, we have a problem," said Hilal Khashan, political science professor at the American University of Beirut (AUB).

"If they are unhappy, that would violate the spirit of the constitution," he said, arguing that Mikati risked "political suicide" if he tried to form a government in defiance of Hariri supporters who consider him the tool of a Hezbollah "coup."

Hariri, who has said his bloc will not join a Mikati-led government, asked his supporters to avoid violence, urging them not to let their anger trump their "commitment to democracy."

Hezbollah leader Sayyed Hassan Nasrallah said his party would back a "national partnership" cabinet formed by Mikati.

RUPTURE WITH TRIBUNAL

His priority is for Lebanon to repudiate the tribunal, which issued still-secret indictments last week that are widely expected to implicate Hezbollah members in Hariri's assassination, a charge the Shi'ite group denies.

Under the aborted Syrian-Saudi deal, even Saad Hariri is believed to have conditionally agreed to cut ties with the court, which gets 49 percent of its funds from Lebanon.