PSNI Chief Constable George Hamilton has rejected claims that the threat of violence at the Irish border after Brexit was being exaggerated.
He told BBC News NI that those who say the PSNI or others, are "overplaying the border and Brexit in policing terms" are "simply wrong".
He said he thought that "anything that re-emphasises the border" presents challenges for policing.
It presents "uncertainty, and issues around identity", he added.
The PSNI is to recruit 102 extra officers by April in preparation for Brexit.
Mr Hamilton said that if the Brexit negotiations resulted in no deal, it would "magnify all the demands and difficulties".
However, he cautioned that even an agreement would not mean "everything's sorted".
Mr Hamilton said: "The terms of that deal may not meet with agreement from everyone.
"So even in a deal scenario, we need to try to work out the likely responses to it and the consequences that might arise."
Mr Hamilton said that dissident republicans who are opposed to the peace process would try to "exploit" any hardening of the border - both "politically and ideologically" and through engaging in organised crime, such as smuggling.
He also said the PSNI (Police Service of Northern Ireland) were mindful of the possibility there could be protests by loyalists if they felt any deal or no-deal created "a perception of insecurity and uncertainty of unionism's position within the UK".
The head of police in the Republic of Ireland, Garda commissioner Drew Harris, said he wanted to make sure that co-operation between his force and the PSNI continued after Brexit.
But he said that required "legal underpinnings" which were currently provided by EU criminal justice treaties.
Mr Harris also highlighted the threat from dissident republicans, saying: "They'd wish to use any difference in the border arrangements as a rallying call to their campaigns."
Mr Hamilton told the BBC there was likely to be a bid to the government for funding for more resources, and he hoped the coming months would bring "more clarity about what the challenges are going to be".