Protesters retreat after throwing stones at riot police and torching a private security vehicle during clashes in central Athens yesterday. A group of youths threw firebombs and other missiles at riot police, who responded with tear gas, but there were no arrests. The incidents marred a planned demonstration by thousands of university students and professors in protest at proposed university reforms. The rally coincided with a 24-hour strike by primary school and kindergarten teachers and a half-day sympathy walkout by civil servants. During the march, a group of youths broke away and threw firebombs in front of the Parliament building in Syntagma Square.