PSNI Chief Constable George Hamilton has said the European Arrest Warrant (EAW) is critical in the fight against crime after EU chief negotiator Michel Barnier warned the UK would be kicked out of the system after Brexit.
Mr Hamilton said the removal of the system, which allows EU members to request the arrest and detention of criminals in other countries without extradition talks, could endanger the safety of communities in Northern Ireland.
The UK wants to stay part of the system when it leaves the EU next March and the loss of the EAW would have serious implications between Northern Ireland and the Republic, particularly in the fight against terrorism and organised crime.
The Chief Constable said: "I have previously stated how important the EAW is to ensuring the safety of communities both in Northern Ireland and across Europe by providing for a quicker, efficient and dynamic response to crime and criminality.
"For the PSNI, the EAW is particularly critical in our continued collaboration with An Garda Siochana and ensuring that the border cannot be used by criminals to evade prosecution.
"We are working with the national working group led by the National Crime Agency and the National Police Chiefs Council to inform and support Government on these critical issues throughout the Brexit process."
Mr Barnier said "facts have consequences" and the UK's decision to leave the EU and the single market meant things could not stay the way they are currently.
He said: "The UK wants to maintain all the benefits of the current relationship, while leaving the EU regulatory, supervision, and application framework. They try to blame us for the consequences of their choice.
"Once again, we will not be drawn into this blame game.
"It would mean wasting time we don't have."
Mr Barnier added that aside from the European Court of Justice, the arrest warrant was also underpinned by the EU Charter of Fundamental Rights and by the concept of EU citizenship.
He added: "Today we know that the UK is not ready to accept the free movement of people, the jurisdiction of the court and the Charter of Fundamental Rights - for the charter, this was confirmed last week by the House of Commons.
"This means that the UK cannot take part in the European Arrest Warrant."
Alliance MLA and former Justice Minister David Ford said the European Arrest Warrant is critical to fighting crime in Ireland.
"It's an essential component of north-south justice, being a crucial part of combating terrorism on both sides of the border," he said.
"Alliance warned before the Brexit referendum of the dangers a result in favour of leaving the EU would bring regarding the future of the warrant and now we are seeing that play out.
"As Justice Minister, I saw first-hand the way in which security co-operation was largely based on European legislation and we can't underestimate the effect the European Arrest Warrant has in tackling the challenges posed.
"The Conservatives claim to be a party of law and order.
"However, through their actions, they are putting in danger one of the key aspects of maintaining that law and order in Northern Ireland.
"Our security cannot be risked in pursuit of Brexit."