Clashes have broken out in several areas of Lebanon following Sunday’s funeral of the senior intelligence official, Wissam al-Hassan.
The most serious confrontations were in the northern city of Tripoli, where at least three people were killed as Sunni and Shia gunmen exchanged fire.
In Beirut, there were clashes between soldiers and armed men in the Sunni Tariq al-Jadida district.
Gen Hassan, a Sunni, was killed by a car bomb in the capital on Friday.
He was the head of the intelligence branch of the Internal Security Forces and an outspoken critic of Syrian President Bashar al-Assad, a member of the Shia-based Alawite sect.
Opposition figures have blamed the Syrian government for the attack.
They have called on Prime Minister Najib Mikati to resign, saying he has failed to protect the country from violence perpetrated by Syria.
Mr Mikati did offer to stand down on Saturday, but President Michel Suleiman asked him to stay on in the national interest.
Children killed
Thousands of people attended Gen Hassan’s state funeral in Beirut, which rapidly became a political rally against both Mr Mikati and Syria.
Friday’s blast occurred in the mainly Christian district of Ashrafiya, in a busy street close to the headquarters of Mr Hariri’s 14 March coalition
Addressing the funeral, former Prime Minister Fouad al-Siniora, a prominent member of the Western-backed 14 March opposition alliance, blamed the government for his death, and said it must stand down, insisting: “No dialogue over the blood of our martyrs.”
A group of angry protesters broke away from the funeral, held at the Rafik Hariri mosque, and attempted to storm the prime minister’s office. Police fired into the air and used tear gas to break up the crowds.
Further clashes were reported overnight and again on Monday morning in the Tariq al-Jadida, a Sunni areas neighbouring a Shia district.
More serious clashes were reported in Tripoli on Sunday evening, where two children were among at least three people killed. Reports say one of the children, a nine-year-old girl, was hit by sniper fire.
Mr Siniora has called for calm and condemned the violence as no way to try to replace a government.
Dozens of people have set up camp outside Mr Mikati’s office building, calling for Mr Mikati’s cabinet – which is dominated by the pro-Syrian Shia Islamist movement Hezbollah and its allies – to stand down.
One of the protesters, Ahmad Jardali, said they were peaceful but wanted the government to go “in order not to have more assassinations and to have security in the country”.
The US has said it will help the Lebanese government with its investigation into the bombing.
Gen Hassan, 47, was close to the 14 March alliance and the family of its leader, former Prime Minister Saad Hariri.
The intelligence chief led an investigation into the 2005 assassination of Mr Hariri’s father, Rafik – for which four Hezbollah members have been indicted by a UN-led tribunal – and had recently organised the arrest of Michel Samaha, a former minister accused of planning a Syrian-sponsored bombing campaign in Lebanon.
Syrian troops withdrew from Lebanon in the wake of Rafik Hariri’s murder, ending a 29-year military presence.
The BBC’s Wyre Davies in Beirut says there are concerns that Damascus is able to reach into Lebanese society both directly and through its allies.