Wednesday's events quickly took on a sectarian tone with clashes in mixed Shi'ite and Sunni neighbourhoods. At least 10 people were wounded.
Sunni Mufti Sheikh Mohammad Rachid Kabbani denounced the actions of "outlawed armed gangs" and appealed to Hezbollah to withdraw its gunmen from Beirut. "The Sunni Muslims in Lebanon are fed up," he said in a televised address to the Lebanese.
Political sources said army commander General Michel Suleiman had rejected a government idea to declare a state of emergency and impose a curfew. Siniora had told Future News television his cabinet was considering such a move.
The Lebanese army, mainly seen as neutral during the crisis, was deployed in Beirut but it refrained from using force to open roads and to stop the clashes.
Hundreds of Hezbollah followers and their allies spent the night manning roadblocks of earth, concrete blocks and old cars.
They kept up their campaign on Thursday, burning more tyres and building up their barricades. Most Beirut residents stayed indoors.
Tension between the government and Hezbollah rose sharply on Tuesday when the cabinet said the group's communication network was "an attack on the sovereignty of the state". Hezbollah said it was part of its security apparatus and had played a major role in its war with Israel in 2006.
Hezbollah was also infuriated by government allegations it was spying on the airport and by the cabinet's decision to remove the head of airport security, a figure close to the opposition, from his post.
Hezbollah has deemed Siniora's cabinet illegitimate since its Shi'ite ministers resigned in 2006 after he rejected demands for veto power against government decisions.
The crisis has paralysed much of the government and left Lebanon without a president for five months.
