Hezbollah militants, some carrying assault rifles or rocket-propelled grenade launchers, patrolled outside Starbucks and other shops in the mostly deserted commercial strips of neighborhoods normally controlled by Sunnis loyal to the U.S.-backed Lebanese government. Masked armed men in civilian clothes set up checkpoints and asked passersby for their identity cards, and Hezbollah forces briefly surrounded the homes of Saad Hariri, Lebanon's top Sunnni lawmaker, and Walid Jumblatt, his Druse ally.

Although government troops soon arrived to guard the politicians' residences, and the Hezbollah gunmen stood down, the Associated Press reported that a satellite television station affiliated with Hariri was forced off the air, and the office of his party's newspaper was set on fire.

Friday's gains by Hezbollah came a day after the leader of the movement accused the government of declaring war on his party.The clashes took on a sectarian cast as mainly Shiite opposition members battled predominantly Sunni supporters of the government. Shiite gunmen tore down posters of Hariri in neighborhoods where he enjoys strong support, the AP reported, and roamed unopposed through streets normally dominated by government supporters.

Christian Lebanese on both sides of the country's political divide largely stayed out of the fighting, and Christian neighborhoods of Beirut were not involved in the clashes.

At the United Nations, special envoy Terje Roed-Larsen warned the Security Council Thursday that the outbreak of fighting was the worst since the country's 1975-1990 civil war. U.S. officials condemned Hezbollah, which is backed by Syria and Iran, and said the United States and other governments would also hold Syria responsible.

The clashes began this week after the government announced it would dismantle a Hezbollah telecommunications network and reassign a Shiite army officer in charge of security at Beirut's international airport.

After a relatively calm morning Thursday, clashes worsened in the afternoon following a speech and news conference by Hezbollah's secretary general, Hasan Nasrallah, who said the party would defend its communications system.

"The government's decisions were a declaration of war, and we have to defend our weapons. . . . Weapons will be used to defend the weapons," he said, demanding that the "black gang" -- a reference to the government -- withdraw its "dark decisions."

Later in the evening, pro-government parliament member Hariri proposed a four-point plan to avoid further escalation, including the election of army commander Gen. Michel Suleiman as president and the resumption of national dialogue. Lebanon's current political crisis started with the resignation of Shiite ministers from the cabinet in 2006 and has left the country without a president since November.

Lebanese politicians say they support Suleiman, but they have been unable to convene parliament in order to elect him.

Hezbollah and Amal, an allied Shiite movement, declared Hariri's initiative unacceptable, insisting that the initiatives in the streets would be suspended only after Nasrallah's conditions had been met...