Loyalist paramilitaries have ordered two Catholic families to leave Antrim town within 72 hours, according to police sources.
The RUC received a message on Wednesday purporting to come from the Ulster Volunteer Force (UVF) in which the two families were accused of antisocial behaviour and told to leave the mixed Styles Estate.
In a statement yesterday, the UVF denied it was responsible for the expulsion orders.
Some of the people threatened are reported to be preparing to flee their homes.
Security sources said one of the families had relatives living in five houses on the estate. According to the family, the threat was affecting seven adults and 12 children.
A local Ulster Unionist councillor, Mr Adrian Watson, described the situation as "dreadful".
A representative of the Progressive Unionist Party in south Antrim, the political wing of the UVF, Mr Ken Wilkinson, said after consultation with the paramilitaries, he was convinced the UVF was not responsible.
Meanwhile, the RUC said yesterday it believed a fire, which caused extensive damage to a grammar school in south Belfast, was started maliciously.
Staff holding a meeting at Rathmore Grammar School on Wednesday night spotted the blaze which started in the basement after arsonists had drilled a hole in the basement door and poured petrol through it.
The SDLP Assembly member for the area, Ms Carmel Hannah, whose four children attend the school, condemned the attack.
A Sinn Fein councillor, Mr Paul Butler, said the attack on Rathmore Grammar had "all the hallmarks of a sectarian attack".
A petrol bomb attack has caused scorch damage to a house in Greencastle at the outskirts of north Belfast. The device damaged a gable wall when it was thrown at the building at about 10 p.m. on Wednesday.
An SDLP delegation held talks with the RUC Chief Constable, Sir Ronnie Flanagan, yesterday to voice their concern about the upsurge in sectarian attacks on nationalists, particularly in the east Antrim area.