Security is to be tightened at schools in Belfast after an alleged threat against teachers by loyalist terrorists.
Police say an anonymous telephone caller, purporting to represent the so-called Red Hand Defenders, warned of action.
Earlier this week, at the height of the disturbances in north Belfast, up to 20 cars belonging to staff at a Catholic secondary school were damaged by six men armed with iron bars.
Representatives of one teachers' union also warned of possible strike action unless the trouble which forced the closure of the Holy Cross school ended.
Classes were also halted at a number of other schools in the area because of fears for the pupils' safety.
Assistant Chief Constable Alan McQuillan said a number of threats against teachers had been made over the past 12 months. Many he said, proved to be hoaxes.
But he added: "In the light of concern about these threats we will be taking special measures which will include increased patrolling."
Meanwhile, north Belfast is reported calm after two nights of rioting and petrol bombing which left more than 80 police officers and troops injured.
Two houses were attacked in the Protestant Twaddell Ave area and one on the Catholic Crumlin Road. Nobody was hurt.