A UK withdrawal from the European Union could make policing in Northern Ireland slower, more complicated and more costly, the head of the Police Service of Northern Ireland (PSNI) has said.
George Hamilton was speaking to MPs on the Northern Ireland affairs committee.
It is investigating how a UK exit from the EU could affect Northern Ireland.
Mr Hamilton said the PSNI would "not take a position on exit or not" and would work with whatever circumstances are in place after the EU referendum.
Voters will go to the polls in June to decide whether the UK should remain a member of the EU.
Asked on whether an exit from the EU would affect policing, Mr Hamilton said: "I think all of this is probably doable with an exit, but it will be slower, complicated and more costly is the view we would take from a practical policing perspective."
But he said the PSNI had a "very good working relationship" with a number of police forces in non-EU countries, "most notably America".
Mr Hamilton, who appeared before the committee with Assistant Chief Constable Will Kerr, also said he did not think the PSNI's link with the Irish police would suffer in the case of an exit from the EU.
He said "the relationships are secure".
He added that if a so-called Brexit - a shorthand term for a UK exit from the EU - took place he was "absolutely sure the quality of the relationship and the professionalism of both organisations would not be diminished".
The committee is examining areas like the economy and the border with the Republic of Ireland.
It has already heard evidence from a wide range of politicians and business leaders.