Sporadic gunfire and the thump of exploding rocket-propelled grenades could be heard through the night in west Beirut, where the fighting was concentrated between Sunni militants loyal to the Western-backed government and supporters of the Hezbollah-led opposition.

At least seven people were reported dead and dozens injured in fierce gunbattles that erupted after Hezbollah chief Hassan Nasrallah declared that a government crackdown on his group was tantamount to a declaration of war.

Armed militants could be seen prowling about or hiding in buildings in the otherwise deserted streets of Beirut as gunfire rang out, in scenes reminiscent of the dark days of the 1975-1990 civil war.

"West Beirut plunges into urban warfare," thundered the French newspaper L'Orient-Le-Jour:

"For the entire country, it is now a question of life or death," an editorial said. "Nasrallah offered the government no other alternative than a humiliating retreat or war."

The international community launched urgent appeals for calm in the deeply divided country amid fears of a descent into chaos after a bitter 18-month power struggle between the rival political factions.

The opposition appeared to be ruling the streets of west Beirut, routing out pro-government militants from many mixed Sunni-Shiite neighbourhoods and moving in on key pro-government media operations.

Future News television, run by the Future Movement of parliamentary majority leader Saad Hariri, was forced to shut down.

"Armed gunmen surrounded the building, stormed into the garage and demanded through the army the shutdown of the station," station head Nadim Moulla told AFP.

The headquarters of the Future movement's Al-Mustaqbal newspaper was also surrounded by gunmen firing rocket-propelled grenades, setting fire to one floor, its managing editor said.

Air traffic was set to be paralyzed for the third straight day with no flights scheduled to land or take off from Beirut international airport, an airport official said, after Hezbollah supporters blocked access with mounds of earth and burning tyres.

The United States delivered a blunt warning to the Iranian- and Syrian-backed Hezbollah to stop its "disruptive activities" while UN Security Council members said they were "deeply concerned" over the crisis.

Nasrallah delivered his defiant speech on Thursday after the government 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 decisions are tantamount to a declaration of war and the start of a war... on behalf of the United States and Israel," Nasrallah charged. "The hand that touches the weapons of the resistance will be cut off."

Hariri, whose father Rafiq Hariri was assassinated in 2005, made a television appeal to try to calm the situation saying the army could be put in charge of the decision on the communication network.

"My appeal to you and to myself as well. the appeal of all Lebanon, is to stop the slide toward civil war, to stop the language of arms and lawlessness."

Underscoring fears of continued instability, people rushed to stores to stockpile food and bread, while the United Arab Emirates began evacuating its nationals from Beirut.

"Hezbollah needs to make a choice: Be a terrorist organisation or be a political party, but quit trying to be both," said US national security council spokesman Gordon Johndroe. "They need to stop their disruptive activities now."

He said US President George W. Bush would discuss the turmoil when he meets Lebanese Prime Minister Fuad Siniora in Egypt next week during a Middle East tour.

The latest unrest erupted on Wednesday during a general strike over price increases and wage demands which quickly degenerated into a confrontation between political rivals.

The long-running political standoff has left the country without a president since November, when pro-Syrian Emile Lahoud stepped down.

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.

Regional powers Egypt and Saudi Arabia voiced support for the Siniora government, and Arab League chief Amr Mussa, who has embarked on several fruitless missions to try to resolve the crisis, urged Lebanon's leaders to avoid any further escalation.

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."

© 2008 Agence France-Presse