Thousands of Hezbollah-led protesters bent on toppling Lebanon's cabinet barricaded roads with blazing tires on Tuesday, provoking clashes with government supporters.
What was planned to be a peaceful nationwide work-stoppage instead turned into the worst violence since Hezbollah and its allies launched a campaign to oust the Prime Minister Fuad Sanoria's Western-supported government two months ago.
Saniora vowed to stand firm against the demonstrators.
"We will stay together against intimidation. We will stand together against strife," he said in a televised speech.
"Today's general strike turned into actions and harassment that overstepped all limits and rekindled memories of times of strife, war and hegemony," Saniora said.
Black smoke rose over the capital Beirut as opposition supporters shut main roads with roadblocks of blazing tires, including those to the port and international airport.
Commuters were stranded and business came to a halt in many parts of the capital.
Aviation officials said the country's only international airport was operating as normal, but that few workers or passengers showed up.
At least three were killed and dozens injured during clashes in central and northern Lebanon, including two bodyguards of a prominent pro-government politician.
Clashes mainly broke out in areas of Beirut and other cities where the loyalties of residents are split between government supporters and opposition forces.
On the coastal highway north of Beirut, near the Christian port city of Jounieh, troops bearing automatic rifles and batons separated hundreds of pro- and anti-government protesters.
Shots were fired in the air, apparently by security forces to scatter the crowds.
But Saniora suggest the government might take stronger measures.
"The duty of the army and security forces does not allow any flexibility or compromise regarding the public interest, order and civic peace," he declared.
The opposition has been camped out since Dec. 1 in front of the prime minister's office and staged several protests to press its demands. But the action has been largely peaceful until now.
Hezbollah's deputy leader, Sheik Naim Kassem, told al-Jazeera television that the opposition would decide later in the day whether to call off the action or continue the escalating campaign.
"It was very successful and a clear message" to the government and its international backers, said Kassem.
Government officials said the protests were tantamount to an attempted coup.
"This will fail as in the past, and the legitimate government of Lebanon will remain steadfast," Telecommunications Minister Marwan Hamadeh told Al-Arabiya television.
Another Cabinet minister, Ahmed Fatfat, expressed concern that violence could erupt between the rival factions.
"The opposition is attempting a coup by force ... This is not a strike. This is military action, a true aggression and I'm afraid this could develop into clashes between citizens," Fatfat, the youth and sports minister, told Al-Arabiya.
The strike has underscored existing political divisions. The anti-Syrian parliamentary majority, consisting of mostly Sunni Muslims, Druse and Christians, backs Saniora and is supported by some powerful outside players, including the U.S., France and Saudi Arabia.
The opposition is led by the pro-Syrian and pro-Iranian Shiite Muslim Hezbollah, and includes also some Druse and Christians.
On Tuesday, the U.S. undersecretary of state for political affairs Nicholas Burns called for Arabs, the U.S. and Europe to throw their support behind Saniora.
"We have indications they will try to go into the streets this week to overturn a democratically elected government, through the rule of people in the streets, through mobs," he said in a speech in Dubai, United Arab Emirates.
The strike comes for a difficult time for the government, as potential donors gather in Paris for an international aid conference which the government hopes will yield billions of dollars for Lebanon's debt-wracked economy.
The clashes prompted Saniora to delay his departure for the conference.
With files from The Associated Press
