BEIRUT: Fierce gunbattles erupted in Beirut on Thursday after Hezbollah chief Hassan Nasrallah charged that a Lebanese government crackdown on his group's activities was tantamount to a "declaration of war."

Lebanon's protracted political crisis was threatening to spiral into a full-blown sectarian conflict, despite urgent appeals for calm in the deeply divided country and a blunt US warning to Hezbollah.

Supporters of the Western-backed government and the Hezbollah-led opposition were engaged in shootouts in several mixed Sunni and Shiite Muslim districts of the capital, with militants using rocket-propelled grenades and machine guns, a security official said.

In scenes reminiscent of the 1974-1990 civil war, Beirut's streets were virtually deserted as loud explosions and gunfire rocked the capital, with television footage showing gunmen, some of them hooded, firing at each other.

There were no reports of casualties, although armed clashes in other towns earlier left at least eight people wounded.

Nasrallah said his powerful Shiite group was ready to use its weapons, in a fiery speech on the second day of anti-government protests which saw supporters of rival factions block roads with burning tyres and force the closure of Lebanon's international airport.

"The (government) decisions are tantamount to a declaration of war and the start of a war... on behalf of the United States and Israel," he charged during a rare press conference via video link.

The government on Tuesday launched a probe into a private communications network run by Hezbollah, which is seen in the West as a terrorist outfit and which critics say has become a "state within a state."

The White House demanded that Hezbollah "stop their disruptive activities," while regional powers Saudi Arabia and Egypt voiced support for the government of Prime Minister Fuad Siniora.

"The hand that touches the weapons of the resistance will be cut off," Nasrallah warned. "We have the right to confront he who starts a war with us by defending our rights and our weapons."

He said Hezbollah was ready for dialogue but demanded the government rescind its measures.

The latest unrest in Lebanon, engulfed in its worst crisis since the civil war, erupted on Wednesday during a general strike over price increases and wage demands.

"If this situation continues, everyone will lose and this will affect the unity of the military," the army command warned.

A security official said that while the army's mission was to maintain order, troops could not intervene to stop the clashes.

Cabinet ministers were meeting to discuss the situation while parliamentary majority leader Saad Hariri was set to hold a press conference at 1700 GMT.

As the crisis escalated, UN Middle East envoy Terje Roed Larsen told the Security Council that Hezbollah's separate paramilitary infrastructure "constitutes a threat to regional peace and security."

Israel, which fought a devastating war with Hezbollah in 2006, said it had no comment on the events in its northern neighbour, with foreign affairs spokesman Arye Mekel bluntly stating: "It's none of our business."

Protesters burned tyres and lit fires along the airport road, which remained blocked by large mounds of earth dumped by Hezbollah supporters, while government loyalists set up roadblocks and set tyres ablaze along the main highway to Syria and between Beirut and the southern coastal city of Sidon.

Many schools and businesses remained shut and flights were cancelled for most of the day although an airport official said eight planes had taken off in the afternoon.

Lebanon's political crisis has left the country without a president since November, when pro-Syrian Emile Lahoud stepped down at the end of his mandate with no elected successor.

While the rival factions have agreed to the election of army chief Michel Sleiman, they disagree on the make-up of the new cabinet and so far 18 sessions of parliament to choose a president have been cancelled.

Hezbollah's ally Amal warned that the situation could get out of hand.

"It is clear the majority is seeking an escalation and wants to push the country toward a civil war," an official told AFP. "What we are trying to do is calm down the situation."

As-Safir newspaper, close to the opposition, said the situation was a "stark reminder for the Lebanese of the dark days of the civil war."

"The two camps have crossed all the red lines and are heading toward an armed confrontation," added Al-Akhbar, also close to the opposition.

Egyptian Foreign Minister Ahmed Abul Gheit repeated Cairo's support for Siniora and implicitly blamed the opposition for the crisis.

"The party that is pushing for confrontation and which persists along this path with disregard for civil peace will surely bear the historic responsibility for its actions," he reportedly told Hariri.

Saudi Arabia also warned those behind the latest incidents to "reconsider their position, and to realise that leading Lebanon towards turmoil will not bring victory to any party except extremist external forces." - AFP/de