Items police believe were to be used to make petrol bombs and paint bombs have been seized in two house searches in Co Armagh.
Two 20-year-old men were arrested during the searches in Portadown on Tuesday night.
There were disturbances in the town on July 15 and 16 and police have said they had received information that more trouble was planned.
They also said security camera footage is being reviewed to identify those involved in the previous violence.
Chief Inspector Anthony McNally said: "These two arrests are in addition to the four arrests made on Friday 15 July.
"With a robust and proactive follow-up inquiry into public disorder on both Friday 15 and Saturday 16 July 2011 now under way, these arrests are a clear indication of our intent to apprehend those behind this mindless violence.
"Our inquiries will continue over the coming days which includes a significant amount of CCTV footage being reviewed to identify those involved, and it is anticipated further arrests will be made."