LONDON -- The third week of nationwide protests in Iran turned particularly violent Sunday when security forces besieged Sharif University, a prominent university in the country, and closed the main gates of the facility where hundreds of students were protesting.Protests, however, soon went beyond the condemnation of the morality police and turned into a movement against the Islamic Republic, with slogans demanding the toppling of the regime.Accusing protesters of making the streets “unsafe” by setting cars and banks on fire, he said people should have waited for the results of the “investigation.”"I say clearly that the riot is designed by America, the Zionist regime and those on their payroll," Khamenei said, alleging that some of the protesters have links to the country’s former monarch or some of its opposition groups.The Islamic Association of Sharif University Students said it invited “students and professors of universities across the country to close their classes as a sign of solidarity with the professors and students of Sharif University.”The call for the strike was received by many university students who kept protesting despite the crackdown on the Sharif University protests.“Nationwide strikes cause psychological pressure on the repressive forces to realize that many people agree with the protesters,” a Health Ministry employee told ABC News."