line militiamen firing tear gas and throwing stones stormed a crowd of thousands of university students protesting for a second day Tuesday, as Iran threatened a tougher crackdown on the opposition after the biggest anti-government demonstrations in months. More than 200 people were arrested in Tehran during protests by tens of thousands at universities nationwide, and Iran's top prosecutor warned further unrest would not be tolerated. He hinted authorities could even pursue the top opposition leader, Mir Hossein Mousavi, an escalation the government has so far balked at in Iran's postelection turmoil. Masked motorcyclists – likely hard-line militiamen – harassed Mousavi at his Tehran office Tuesday. An angry Mousavi confronted them, daring them, “Kill me!” before being hustled away by aides, according to pro-opposition Web sites. Authorities appear concerned that the protest movement could pick up new steam after Monday's demonstrations. A fierce crackdown since the summer crushed the mass protests that erupted after June's disputed presidential election. But Monday's unrest showed how students have revitalized the movement. They showed an increased boldness, openly breaking the biggest taboo in Iran, burning pictures of Supreme Leader Ayatollah Ali Khamenei and chanting slogans against him. The protests spilled over into a second day Tuesday.