Hezbollah-led protesters burned tires and cars and clashed with government supporters Tuesday, paralyzing Beirut and areas across Lebanon in the worst violence yet in the pro-Iranian group’s campaign to topple U.S.-backed Prime Minister Fuad Saniora. At least three people were killed and dozens injured as the two camps battled each other around street barricades with stone-throwing and in some cases gunfire. Black smoke poured into the sky over Beirut from burning roadblocks. The fighting quickly took on a dangerous sectarian tone in a country whose divided communities fought a bloody 1975-1990 civil war. Gunmen from neighboring districts in the northern city of Tripoli — one largely Sunni Muslim, the other largely Alawites, a Shiite Muslim offshoot — fought each other, causing two of the fatalities.