Four arrested after Tripoli Christmas tree is set ablaze in
northern Lebanon

The attack on the northern city's main square came after the assailants smashed the windows of the office of a Sunni Muslim religious leader in Tripoli, Lebanon's official news agency and the military said.

The violence indicated that tensions that recently gripped the Lebanese capital, Beirut, fuelled by an online video deemed offensive to the country's Shia Muslims are spreading to the the country's predominantly-Sunni city.

A mob of men on motorcycles gathered outside the home of Sunni Mufti Sheik Malek al-Shaar and rioted, "used profanity" and smashed property, the military said. The mob then moved to the square and threw fire bombs at the Christmas tree, setting it ablaze.

The tree has since been replaced by another put together by local activists in the form of the flag of Lebanon, according to pictures on social media platforms.

On Tuesday, anger boiled over in Beirut after the offensive video was widely circulated online.

It showed a Sunni resident of Tripoli railing against the leaders of the country's two main Shia groups, Hezbollah and Amal, and religious Shia figures and using expletives. 

Their supporters descended on a protest camp in Beirut as security forces intervened to push them back, setting off hours of pitched street battles.

Angry assailants also attacked protest camps in the northern district Hermel and in the southern Sidon and Nabatiyeh on Tuesday.

The violence threatened to plunge Lebanon further into chaos and ignite sectarian strife amid two months of anti-government protests and a spiralling financial crisis.

The daily An-Nahar said the assailants in Tripoli were angered because the Sunni mufti, al-Shaar, had called the powerful Shia parliament speaker and head of Amal, Nabih Berri, to apologise for the video.

Supporters of Hezbollah and its close ally, the Amal movement, have been intolerant of the protesters' criticism of their leaders and have tried for days, even before the video emerged, to attack the protest camps.

On Wednesday, security forces set up concrete barriers at entrances to Beirut's Riad Solh Square, a main protest site repeatedly attacked by supporters of the two groups.

The anti-government protests, which erupted in mid-October, have spared no Lebanese politician, accusing the ruling elite of corruption and mismanagement, and calling for a government of independents.

They have largely been peaceful, sparked by an intensifying economic crisis. 

Berri, the parliament speaker, and outgoing Prime Minister Saad Hariri met on Tuesday and urged the Lebanese not to be "drawn toward strife" and adding that some parties they didn't name are working to incite violence in the country.

Agencies contributed to this report.

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