Thousands of Sunnis waved flags and burned tires and a van belonging to Al-Jazeera on Tuesday in a "day of rage" to protest against gains by the Shiite group Hezbollah, which is on the brink of controlling Lebanon's next government.
On Tuesday, Lebanon's president formally appointed a Hezbollah-backed candidate as prime minister-designate and asked him to form a new government.
Billionaire businessman and former premier Najib Mikati won a majority of parliament support in two days of voting, defeating Western-backed Prime Minister Saad Hariri as the candidate for the next prime minister.
Hezbollah's Sunni rivals held protests in different parts of Lebanon, including Tripoli, 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.
For the most part in Beirut the gatherings were localised and not hugely disruptive.
The largest gathering was in the northern city of Tripoli, a predominantly Sunni area, 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.
The protests come one day after the Iranian-backed Hezbollah secured support in parliament to name its own candidate, former premier Najib Mikati, for the next prime minister.
The majority of Lebanese lawmakers voted to support Mikati.
By the end of Tuesday's voting, he had 68 votes. Caretaker Prime Minister Saad Hariri had 60.
The Shiite group is now in position to control the next government, which could give it an unprecedented level of political power in Lebanon
The group's Western-backed opponents maintain that having an Iranian proxy in control of Lebanon's government would be disastrous and lead to international isolation.
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.
Mikati urged calm on Tuesday and said he wanted to represent all of Lebanon.
Hezbollah brought down Hariri's Western-backed government on January 12 when he refused the group's demand to cease cooperation with a UN-backed tribunal investigating the 2005 assassination of his father, former Prime Minister Rafik Hariri.
Hezbollah, which denies any role in the killing, is widely expected to be indicted.
The group 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 favoured a unity government.
Hariri said on Monday he will not join a government headed by a Hezbollah-backed candidate.
Hariri's coalition issued a statement last week saying Hezbollah is trying to turn Lebanon into an "Iranian base" and was using intimidation to get its way.
Hezbollah has emphasised that the group brought down Lebanon's government democratically and without resorting to violence.
Even though Hezbollah backed him, Mikati is seen as a relatively neutral figure who enjoys good relations with both Syrian President Bashar Assad and Hariri.
The United States, which has poured in 720 (m) million US dollars 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 on Monday that continuing US support for Lebanon would be "problematic" if Hezbollah takes a dominant role in the government, though he declined to say what the US would do if Hezbollah's candidate becomes prime minister.