BEIRUT, Lebanon &

Shiite Hezbollah supporters and the Lebanese government's Sunni backers clashed with machine guns and rocket-propelled grenades today in battles that spread through Beirut's streets soon after Hezbollah's leader vowed to fight any attempt to disarm his men.




The violence first erupted in Muslim West Beirut, where masked gunmen on street corners opened fire along Corniche Mazraa, a major thoroughfare that has become a demarcation line between the two sides. There was also fighting in the nearby Ras el-Nabeh area. There was no immediate word on casualties.




The violence spread to Khandaq el-Ghamiq, a neighborhood adjacent to downtown, which is home to the government's offices. Shootings and explosions were reported by witnesses and television stations in the Aisha Bakkar neighborhood near the office of Lebanon's Sunni spiritual leader, who is allied with the government. Gunfire and explosions were also heard in a nearby district where the opposition-aligned parliament speaker has his official residence.




Troops in armored carriers had earlier moved in to West Beirut to separate people who were trading insults and throwing stones at each other, but the troops did not attempt to stop the street battles that then broke out.




The army, which has been struggling to contain the disturbances, warned of the consequences to the country and the military.




"The continuation of the situation as is is a clear loss for all and harms the unity of the military institution," a statement said.




The army has largely stayed out of the broader political struggle between Hezbollah and the government for fear of exacerbating the situation. The army's commander is the two factions' consensus candidate for president.




Gen. Michel Suleiman so far has advised the government not to declare a state of emergency.




The clashes came close on the heels of a defiant speech by Hezbollah leader Hassan Nasrallah, who said his organization would respond with force to any attacks.




"Those who try to arrest us, we will arrest them," he said. "Those who shoot at us, we will shoot at them. The hand raised against us, we will cut it off."




It was the second day of fighting that has turned some city neighborhoods into battlegrounds and spilled over to other parts of the country.




The violence appeared to begin as a test of wills between political rivals who have been locked in a 17-month power struggle for control of the government. It now could be degenerating into a wider and deadlier sectarian conflict, with the Sunnis' spiritual leader denouncing Hezbollah and appealing to a largely Sunni Islamic world to intervene.




The rivals have failed to agree on electing a president, leaving the country without a head of state since November.




The latest round of tensions was sparked by the government's decision earlier this week to confront Hezbollah by replacing the Beirut airport security chief for alleged ties to the Shiite militants.




The government also declared Hezbollah's private communications network to be illegal.




Hezbollah and leaders of the 1.2-million-strong Shiite community, believed to be Lebanon's largest sect, rejected the decisions, and the airport security chief kept his job.




Supporters of the Hezbollah-led opposition blocked roads in the capital on Wednesday to enforce a strike called by labor unions protesting the government's economic policies and demanding pay raises.




The strike quickly escalated into street confrontations between supporters of the rival camps. About a dozen people were injured, mostly by stones, but no deaths were reported.




Today, the violence spread outside the capital. Sunnis and Shiites exchanged gunfire in the village of Saadnayel in the eastern Bekaa Valley. Four people were injured, said security officials, speaking on condition of anonymity in line with military regulations.




The area is on a major crossroads linking the Shiite areas of Baalbek, a Hezbollah stronghold, with central Lebanon and Beirut.




Nasrallah claimed Hezbollah's secure network of primitive private land lines helped the guerrillas fight Israel's high-tech army in the 2006 summer war.




He said the telecommunications network was "the most important part of the weapons of the resistance" and added Hezbollah had a duty to defend those weapons.




"The decision is tantamount to a declaration of war ... on the resistance and its weapons in the interest of America and Israel," Nasrallah said.




Hezbollah supporters kept the road to the country's only airport blocked, effectively closing the airport for a second day.




The clashes have brought back memories of the devastating 1975-1990 civil war that has left lasting scars on Lebanon.




Beirut residents are now seeing fresh demarcation lines, burning tires and roadblocks.