Lebanon President Michel Suleiman appointed Hezbollah-backed Najib Mikati as the country's new prime minister on Tuesday, a move that  triggered mass protests amongst supporters of caretaker Prime Minister Saad Hariri.

Najib Mikati, a Sunni Muslim from Tripoli, won the nomination of 68 members of parliament of the country's 128-member assembly.

Speaking after the appointment, Mikati said he would start talks to form the government on Thursday and urged all Lebanese factions to overcome their differences.

Hezbollah and its allies toppled the government of the Western-backed Hariri two weeks ago, after he refused to reject an international tribunal into the 2005 assassination of his father, former prime minister Rafik Hariri. The United Nations-backed tribunal is widely expected to name members of Hezbollah in upcoming indictments, which many fear could reignite hostilities between Lebanon's rival Shi'ite and Sunni Muslims.

The vote caps Hezbollah's steady rise over the past few decades from a resistance group fighting Israel to Lebanon's most powerful military and political force. The events of the past few days drew warnings from the U.S. that its support for Lebanon could be in jeopardy, demonstrating the risks of international isolation if Hezbollah pushes its power too far.

Hezbollah's Sunni rivals, who support Hariri, demonstrated for a second day across the country including the capital Beirut and the main highway linking the capital with the southern port city of Sidon. A senior military official said several armed men fired in the air in west Beirut, but the army intervened and dispersed them.

The largest gathering Tuesday was in the northern city of Tripoli, a predominantly Sunni area and a hotbed of fundamentalists where thousands of people converged at a major square. Al-Jazeera said none of its crew was injured when protesters attacked the station's van.

Soldiers also clashed with demonstrators in the town of Naameh, south of Beirut, and two civilians were wounded, security officials said.

Hariri thanked people for their support but called for restraint.

"I understand your emotions ... but this rage should not lead us to what is against our morals, faith and beliefs," he said.

Many fear Lebanon's political crisis could re-ignite sectarian fighting similar to Shiite-Sunni street clashes that killed 81 people in Beirut in 2008. But besides the protest in Tripoli, the gatherings Tuesday were mostly localized and not hugely disruptive.

Mikati urged calm Tuesday and said he wanted to represent all of Lebanon.

"This is a democratic process," Mikati told reporters. "I want to rescue my country."

Hezbollah can now either form its own government, leaving Hariri and his allies to become the opposition, or it can try to persuade Hariri to join a national unity government. In a speech Sunday night, Hezbollah leader Sheik Hassan Nasrallah said he favored a unity government.

Hariri said Monday he will not join a government headed by a Hezbollah-backed candidate. Hariri's Future bloc declared a day of peaceful protests Tuesday - but called it a day of rage and played on the sectarian dimension of the conflict.

The United States, which has poured in $720 million in military aid since 2006, has tried to move Lebanon firmly into a Western sphere and end the influence of Hezbollah, Syria and Iran.

State Department spokesman P.J. Crowley warned Monday that continuing U.S. support for Lebanon would be problematic if Hezbollah takes a dominant role in the government, though he declined to say what the U.S. would do if Hezbollah's candidate becomes prime minister.