The Lebanese army has carried out raids in the northern city of Tripoli, searching homes of individuals with alleged links to the Islamic State of Iraq and the Levant (ISIL) and other groups.

The army said 20 armed suspects had been arrested since Friday night and at least eight people, including six soldiers, killed in fighting between troops and fighters.

Saturday's raids came after fierce clashes overnight in and around the city's historic market, or souq.

Security officials said two civilian bystanders, identified as father and son, were killed in the violence that began on Friday night after an army patrol was attacked in the market area.

An unknown number of fighters that the army said were linked to ISIL were also killed.

Twenty people, including a Lebanese newspaper reporter, were injured, officials said.

Tripoli - and several other parts of Lebanon - has been hit by sporadic violence since the start of the war in neighbouring Syria in 2011.

Shelling and gunfire

Gun battles erupted on Saturday evening in the Sunni Bab al-Tabbaneh neighbourhood after an army patrol was attacked, the National News Agency reported.

No casualties were reported.

During the overnight fighting, an AFP journalist reported shelling and heavy gunfire as the army launched its assault on the fighters' positions in the souq area.

A security official told the news agency that most of the fighters were believed to be Lebanese.

"Some of them are Islamists, while others are wanted thugs," he said.

Tripoli has seen repeated clashes between Sunni fighters sympathetic to Syrian rebels and Alawites who back the Syrian regime.

Fighters in the city have also carried out multiple attacks against the Lebanese army, accusing it of cooperating with the Shia group Hezbollah, which has sent thousands of fighters to Syria to support President Bashar al-Assad's forces.

The latest clashes occurred just days after Lebanese soldiers killed at least two men and arrested several others during a raid on an apartment in the northern town of Asoun.

Among the arrested was Ahmad Salim Mikati, who the army accuses of recruiting young Lebanese to join ISIL.

The fighters involved in the souq clashes were calling for his immediate release.

It was the first time since the civil war erupted in Syria that violence in Tripoli had spread to the souq, which is on the shortlist for possible nomination as a UNESCO world heritage site.

Many of the shops in the covered market, with narrow allies, have been burned down in the fighting.