Violence mars Pakistani anti-government protest LAHORE, Pakistan Pakistan's opposition leader defied house arrest on Sunday to lead anti-government protests that briefly turned violent before becoming a jubilant show of force against the country's pro-Western president. Opposition leader Nawaz Sharif called the mass rally a "prelude to a revolution." The power struggle between the former prime minister and President Asif Ali Zardari threatens to paralyze the government and, alarmingly for the U.S., distract the nuclear-armed country from its fight against Taliban militants operating along the Afghan border. Hundreds of police surrounded Sharif's residence in Lahore, carrying an order for his house arrest, party spokesman Pervaiz Rasheed said. But Sharif, who denounced the order as illegal, later left the house in a convoy of vehicles and headed into town. Riot police had earlier fought running battles with stone-throwing protesters, turning the downtown into a battle zone littered with rocks and clouded with tear gas and smoke. A mob smashed windows of buses parked along the route of Sharif's convoy. But by evening the mood was festive as police pulled back, and thousands of flag-waving supporters and cheering lawyers turned out to cheer Sharif, a local favorite. "People have responded very overwhelmingly to the call of the hour, and I am thankful to the nation," Sharif told Geo television by phone from his car. "This is a prelude to a revolution." Washington worries that the crisis will further destabilize the shaky the year-old government and prevent it from being an effective ally in the fight against insurgents in neighboring Afghanistan. Suspected militants attacked a transport terminal in northwestern Pakistan used to supply NATO troops in Afghanistan before dawn on Sunday and torched dozens of containers and military vehicles, police said. The gathering in Lahore was the biggest yet in the buildup to plans for a mass sit-in in front of Parliament in the capital on Monday. The government has refused permission for the indefinite sit-in, arguing that it would paralyze the government and present a target for terrorists. It has put the army on alert in case the unrest gets out of hand. Though Sharif, his politician brother and scores of other opposition party members were initially ordered under house arrest, Sharif was allowed to leave his residence unchallenged.