Thousands of Lebanese troops and police fanned out in Beirut on Friday to tighten security hours before a Hezbollah-led opposition protest aimed at bringing down the Western-backed government.
Pro-Syrian Hezbollah and its allies have called on Lebanese from across the country to take part in the protest to force out the government. It is due to start at 3 pm and will be followed by an indefinite sit-in.
Large numbers of security forces, backed by armoured personnel carriers, deployed in central Beirut, where heavy turnout for the protest is expected. The forces also deployed at the capital's entrances.
"The attempt for a political coup starts today," the pro-government Al-Mustaqbal newspaper said in its front-page headline.
"The moment of truth is upon us... the birth of free, sovereign Lebanon," pro-opposition Ad Diyar's headline read.
Hezbollah, which is backed by Syria and Iran, has branded the government of Prime Minister Fouad Siniora a US puppet.
The anti-Syrian politicians who control the cabinet say the Shi'ite Muslim group and its allies want to stage a coup.
Siniora said on Thursday his government would not stand down.
"Fellow Lebanese we have ahead of us decisive days for Lebanon and its future...," Siniora said in a live broadcast.
"We will not allow the coup against the democratic system, its rules and institutions."
After the speech, celebratory gunfire was heard in Sunni Muslim Beirut districts loyal to Saad al-Hariri, a prominent anti-Syrian leader close to Siniora. Hariri supporters took to the streets waving Lebanese flags.
Supporters of Hezbollah and its allies — the Shi'ite Amal Movement and the Free Patriotic Movement of Christian leader Michel Aoun — also drove through the streets of central Beirut flying their groups' flags.
Many Lebanese fear that large protests could spill over into violence. Tension between Sunni Muslims and Shi'ites is high, as is bad feeling between Christians who support leaders allied to the rival camps.
The opposition has repeatedly said they aim to hold peaceful protests. The army has said it will be neutral but intervene to stop violence or attempts to storm government buildings.
The opposition accuses the majority in cabinet of monopolising power and says protests are their only option.
Hezbollah has repeatedly criticised Siniora's cabinet over what it says was its failure to back Hezbollah during a July-August war with Israel, accusing some of the majority leaders of hoping at the time his group would be crushed.
The anti-Syrian camp accuses the opposition of aiming to bring down the government to derail an international tribunal to try suspects in the assassination of former Prime Minister Rafik al-Hariri, whose killing many Lebanese blame on Damascus.
Syria denied involvement but was forced to pull its troops from Lebanon by international pressure led by the United States and France.
Siniora's government was weakened last month by the resignation of six opposition ministers and the November 21 assassination of anti-Syrian cabinet minister Pierre Gemayel.
If two more ministers were to resign or die, the government would automatically fall. Hariri and his allies have blamed Syria for Gemayel's killing, as they blamed it for the slaying of Rafik al-Hariri last year.
A UN inquiry has implicated Syrian and Lebanese security officials in the Hariri assassination.
Siniora's depleted cabinet approved UN plans last week for the special court for the Hariri trial.