Police in north Belfast fired seven baton rounds during what they described as "serious disturbances" in the Mount Vernon area last night.
A crowd of around 200 loyalists attacked police officers last night as they arrested a local woman. A quantity of ammunition was recovered in the arrest.
One police officer was injured and a number of police vehicles were badly damaged.
A Police Service of Northern Ireland spokesman said they were attacked with breeze blocks, pieces of concrete and other missiles - which were thrown from the roof of a flat complex.
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A number of suspect devices, later found to be hoaxes, were destroyed by the British Army in controlled explosions.