Gunmen loyal to opposite sides in neighbouring Syria's civil war battled in the streets of northern Lebanon today, and the death toll from two days of fighting was at least five killed and 45 wounded, according to officials.

Tripoli, Lebanon

The Lebanese army fanned out in the city of Tripoli to calm the fighting, with soldiers patrolling the streets in armored personnel carriers and manning checkpoints. Authorities closed major roads because of sniper fire.

The fighting comes at a time of deep uncertainty in Syria, with rebels closing in on President Bashar al-Assad's seat of power in Damascus.

UN Secretary General Ban Ki-moon on Wednesday urged Syria's regime against using its stockpile of chemical weapons, warning of "huge consequences" if Assad resorts to such weapons of mass destruction.

"I again urge in the strongest possible terms that they must not consider using this kind of deadly weapons of mass destruction," Ban told The Associated Press, speaking on the sidelines of a climate conference in Qatar.

Syria has been careful not to confirm that it has chemical weapons, but the regime insists it would never use them against the Syrian people.

Ban also suggested that he would not favour an asylum deal for the Syrian leader as a way to end the country's civil war and cautioned that the UN doesn't allow anyone "impunity." 

Assad has vowed to "live and die" in Syria, but as the violence grinds on, there is speculation that he might seek asylum.

Tripoli tensions started last week

The Syrian conflict has spilled over into Turkey, Israel and Jordan over the past 20 months, but Lebanon is particularly vulnerable.  The countries share a complex web of political and sectarian ties and rivalries that are easily enflamed. Lebanon, a country plagued by decades of strife, has been on edge since the uprising in Syria began, and deadly clashes between pro- and anti-Assad Lebanese groups have erupted on several occasions.

U.S. aims to blunt extremists

The Obama administration is preparing to designate Jabhat al-Nusra, a Syrian rebel group with alleged ties to al-Qaeda, as a foreign terrorist organization, said U.S. officials.

The step is aimed at blunting the influence of extremists within the Syrian opposition. It would freeze any assets that the group's members have in U.S. jurisdictions and bar Americans from providing the group with material support.

Jabhat al-Nusra has claimed responsibility for suicide bombings and other attacks on Syrian government targets. Its activity has raised fears of a growing Islamic militant element among the opposition.

The officials spoke to the Associated Press on condition of anonymity because they were not authorized to preview the designation — expected to be announced next week — publicly.

Tensions in Tripoli have been mounting since last week, when reports emerged that some 17 Lebanese Sunni fighters were killed inside Syria, apparently after they joined the rebellion against Assad. The bodies of some of the men were later shown on Syrian state TV.

On Wednesday, Lebanese Foreign Minister Adnan Mansour was informed by Syrian Ambassador Ali Abdul Karim Ali that Syria had agreed to repatriate the men's bodies. Lebanon's National News Agency said the countries would soon discuss how to hand over the bodies.

Anti-Syrian politicians in Lebanon have criticized the Hezbollah-led government for what they call a lack of effort to get the bodies back. Lebanon's Hezbollah supports Assad.

The sounds of gunfire and explosions echoed near the clashing neighbourhoods, and police closed roads leading to the area. Nearby cars raced to dodge sniper fire.

Lebanese soldiers parked tanks on a bridge and in a roundabout near the area and patrolled in dozens of armoured vehicles, but did not enter the neighbourhoods themselves to try to stop the clashes.

Lebanese security officials said at least five people have been killed and 45 wounded since Tuesday. They asked that their names not be published because they are not authorized to speak publicly.

The fighting in Lebanon pits the Sunni neighbourhood of Bab Tabbaneh, which supports Syria's rebels, and the adjacent Alawite neighbourhood of Jabal Mohsen, which supports Assad.

Syrian rebels are predominantly Sunni. Assad and his inner circle are dominated by Alawites, an offshoot of Shiite Islam.

Violence continues around Damascus

Fighting continued around Syria on Wednesday, with rebels clashing with government troops around the capital, Damascus, and elsewhere.

Government forces shelled and flew fighter jets over a number of restive areas south, east and north of the capital, clashing with rebels in the eastern suburbs of Zamalka and Arbeen, according to the Britain-based Syrian Observatory for Human Rights. At least two rebel fighters were killed in clashes and three civilians killed in government shelling, said the group, which relies on contacts inside Syria.

'They must not consider using this kind of deadly weapons of mass destruction.' —UN Secretary General Ban Ki-moon

In the north, a Syrian jet bombed the rebel-held town of Tal Abyad, near the Turkish border, while rebels responded with anti-aircraft fire, Turkey's state-run Anadolu agency said. At least two wounded people were brought to the Turkish border town of Akcakale for treatment.

An activist video from the northern province of Idlib showed residents of the village of Talmanis digging through rubble in search of survivors after a government airstrike. The video then shows bodies lying in the back of a pickup truck while an off-camera voice says five people from the same family were killed in a rocket attack from a nearby army base that rebels have repeatedly attacked.

The videos appeared genuine and corresponded to other reports on the incidents. The Syrian government greatly restricts journalistic access to the country, making independent authentication of events nearly impossible.

Syria's uprising began with peaceful protests in March 2011 and later escalated into a civil war that the opposition says has killed more than 40,000 people.