A pipe-bomb was left at the gates of a Catholic school in north Belfast over the weekend.
Part of Fortwilliam Park was closed after the device was found at the gates of Dominican College.
Last week the same school was disrupted while a controlled explosion was carried out on a suspicious device left outside.
Sinn Féin north Belfast councillor Danny Lavery condemned the incident.
``It is completely unacceptable. Those responsible are targeting the easiest and most vulnerable places,'' he said.
``Schools should be treated with respect and left alone as places where our children go to get their education.
``Those responsible have no support and the vast majority of the community would prefer to see schools left untouched by sectarianism.''
A number of schools have been targeted in the last few weeks, including Holy Cross Primary School for girls and an Irish Language nursery school, which was attacked by arsonists.
Meanwhile, there have been attacks again on the McClure Street area of south Belfast. A number of nationalist youths were injured during clashes with loyalists throwing firworks and other missiles.
Former Sinn Féin mayor of Belfast Alex Maskey said trouble in the area was becoming a nightly occurrence.
``I would like to appeal again to loyalist and unionist representatives to bring an end to this,'' he said. ``Local republicans are working hard to keep people away from this area.''
``I am concerned there is a sinister agenda at work here because in recent weeks we have seen an increase in attacks on the nationalist community in McClure Street.''