The Ulster Defence Association has been blamed for an attack along the peaceline in north Belfast in which the homes of 20 Catholics were pelted with stones and paint-bombs.
Windows of houses and cars in the Limestone Road area were targeted.
About 50 armed loyalists arrived in the area in minibuses around 7.30 a.m. yesterday. Residents said they waved guns in the air during the 15-minute assault on Clanchatton and Newington streets.
The loyalists then drove off towards the loyalist Tigers Bay area. Residents and Sinn Fein blamed the UDA for the attack. A Sinn Fein councillor, Mr Gerard Brophy, said the UDA was trying to provoke retaliation and appealed to nationalists not to be drawn into conflict.
The Loyalist Volunteer Force has joined the UDA in threatening to shoot anyone attacking Protestant homes. In a statement at the weekend, it said such attacks would not be tolerated.
Last week the UDA, using its Ulster Freedom Fighters covername, warned that it would break its ceasefire to defend Protestant areas under attack from nationalists.
The UDA first issued the threat in June but suspended it a few days later after political pressure. However, it reinstated it again last Thursday after recent attacks on Protestant homes in which the windows of cars and house were broken.
The UDA blamed republicans. Sinn Fein has denied republican involvement.
Meanwhile, loyalists are believed to have been responsible for a pipe-bomb attack on a house in Ballymoney, Co Antrim, early yesterday.
The device was put through the letter-box of the house on Drumlee Road. It was defused by British army bomb experts.
In Carrickfergus, Co Antrim, shots were fired through the window of a house on Saturday night. No one was injured in the attack in the Northlands area. Loyalists are understood to have been responsible.
Loyalist involvement is also suspected in a petrol and paint-bomb attack on a house at Thorburn Road, off the Serpentine Road, in north Belfast. No one was hurt.
Meanwhile, a man is in hospital after a "punishment" attack in Strabane, Co Derry. He was visiting a flat in Lisnafinn Park when he was dragged outside by several men and beaten with sticks. He was then shot in the knees. Republicans are believed to have been responsible.