Arrests have been made and fixed penalty notices handed out at a protest against coronavirus restrictions in the grounds of Stormont estate in east Belfast.
The PSNI said more than 300 people gathered at the demonstration against the new regulations in NI on Sunday.
The new restrictions came into force on Friday evening.
Ass Ch Cons Alan Todd said police engaged with the organisers "before and during the protest".
"Unfortunately both the organisers and participants did not cooperate with these requests and continued in breach of the regulations," he said.
The PSNI said the numbers in attendance and the "lack of social distancing in the crowd were in stark contrast with assurances given to police by the organisers".
Follow-up enquiries to try to "identify others who may have committed offences" will be made.
"As I have said previously, in other times, we would work with organisers and protestors to facilitate lawful and peaceful protests, however, these are not ordinary times," said Ass Ch Cons Todd.
"The health protection regulations, particularly at this time with increased restrictions in place, are there to protect us all during this pandemic and it is everyone's responsibility to adhere to them to protect our society," he added.