Riot police are seen during clashes with demonstrators in central Athens, Greece, Dec 6, 2012. A student protest rally in Athens to commemorate the death of a teenager by police fire in 2008 ended with minor clashes on Thursday. (Xinhua/Marios Lolos)

Riot police are seen during clashes with demonstrators in central Athens, Greece, Dec 6, 2012. A student protest rally in Athens to commemorate the death of a teenager by police fire in 2008 ended with minor clashes on Thursday. (Xinhua/Marios Lolos)

Demonstrators are seen during clashes with riot police in central Athens, Greece, Dec 6, 2012. A student protest rally in Athens to commemorate the death of a teenager by police fire in 2008 ended with minor clashes on Thursday. (Xinhua/Marios Lolos)

A demonstrator is seen during clashes with riot police in central Athens, Greece, Dec 6, 2012. A student protest rally in Athens to commemorate the death of a teenager by police fire in 2008 ended with minor clashes on Thursday. (Xinhua/Marios Lolos)

Riot police are seen during clashes with demonstrators in central Athens, Greece, Dec 6, 2012. A student protest rally in Athens to commemorate the death of a teenager by police fire in 2008 ended with minor clashes on Thursday. (Xinhua/Marios Lolos)