Tension between youths and police flared up again yesterday with clashes erupting outside the capital's central police headquarters, as pupils and university students staged sit-ins at hundreds of schools and faculties across the country. Hundreds of young protesters pelted riot officers with flour and other objects outside the central police offices on Alexandras Avenue, while officers responded with tear gas. Some 2,000 youths at the rally, protesting the police killing of a 15-year-old boy and proposed education reforms, blocked the road and set fire to trash bins. Police said they detained two protesters but there were no reports of injuries. In Kallithea, southern Athens, a group of around 200 youths also clashed with police outside a police station. Many of the demonstrators were schoolchildren. There were small-scale disturbances in Piraeus as well and in nearby Korydallos, where some 300 pupils rallied outside local jails and jeered at police who fired tear gas to disperse them. There were also peaceful rallies, with pupils marching through the city center and protesting outside Athens's main court complex, where four people arrested during last week's riots were ordered to be held in custody. Although many protesters held banners in memory of Alexis Grigoropoulos, the boy killed in Exarchia the Saturday before last by a police bullet, there was a general sense that the protests are shifting from anger at police tactics to exasperation with the government's policies, particularly those affecting education. According to teachers' unions, some 600 schools were under occupation by pupils yesterday. Students also took over about 150 university faculties across the country. Students are to meet today to discuss future action. One rally is due to begin in central Omonia Square at 6 p.m. tomorrow and another two are planned for Thursday. Rallies are also planned for Thessaloniki and other cities. In a related development yesterday, with the results of ballistics tests and autopsy on Grigoropoulos still pending, Alexis Kougias, the lawyer representing the two officers implicated in the boy's killing, asked that his clients be released. The two officers, one charged with murder and the other as an accomplice, are being detained at the Domoko jail, in central Greece.