At least three Catholic families in Armagh received a bullet through the post today.
Police blamed loyalists and said they were treating it as "naked sectarian intimidation" and appealed for the community to pull together in rejecting such activity.
The bullets were delivered to the families, all living in mixed areas of Armagh city, in the morning mail. Each was wrapped in a piece of paper with the message "24 Hours" scrawled on it.
The intimidation came as tensions continued to rise across the North ahead of this weekend's disputed Drumcree parade and in the wake of yesterday's murder of teenage Catholic Mr Ciaran Cummings as he waited for a lift to work in Antrim.
Condemning the threats, RUC Supt Bob Moore said: "This is despicable, and blatant sectarian intimidation. I call on the community to reject those responsible and pull together."
Elsewhere, a Catholic man escaped when a petrol bomb was thrown into a bedroom of his flat in the Co Antrim seaside town of Portrush.
He was woken by the sound of breaking glass as the device landed in his home at Glenanna Drive at 2 a.m. and managed to get out before the fire, later put out by the fire service, took hold.
Earlier in Carrickfergus, Co Antrim, there was an arson attack on St Nicholas’s Parish Church in Minorca Place. A fire was started inside the church at about 2.30 a.m. It was quickly put out and there was no serious damage.
PA