Lebanese security officials say angry demonstrators have closed roads around the country to protest against a car bombing that killed a top security official and seven others on Friday.

Dozens were also wounded when the car bomb exploded in Beirut during rush hour.

Lebanon's government declared a national day of mourning on Saturday for the victims that included Brigadier General Wissam al-Hassan, head of the intelligence division of Lebanon's domestic security forces.

There has been a heightened military presence in the capital since the explosion, with armoured personnel carriers and soldiers deployed on the streets.

Protesters have closed roads in several cities including Beirut, the southern city of Sidon and the northern city of Tripoli.

The road linking central Beirut with the city's international airport has been closed, as well as the road that links the capital with Syria.