(This May 31 story corrects to show Mark Lindsay is chairman of police federation, not police service.)

BELFAST (Reuters) - Northern Ireland’s police will ask the British government for more officers to help secure the province’s border with Ireland after Britain leaves the European Union, the head of the police service said on Thursday.

Authorities on both sides of the now-open frontier fear a return to a hard border, complete with customs and other checks, could be a target for militant groups behind the violence that afflicted Northern Ireland until a peace deal in the late 1990s.

“A business case is being prepared which will develop a number of scenarios that will present to government the need for some form of uplift in police numbers and other investments to enable us to fulfill our responsibilities post-Brexit,” Police Service of Northern Ireland (PSNI) Chief Constable George Hamilton said in a statement.

“At this time we are not prepare to get into specific numbers, and I don’t want to second-guess the business case, but it will certainly need to be a significant uplift.”

Mark Lindsay, chairman of the Northern Ireland Police Federation (PFNI) group that represents officers, told a conference earlier on Thursday that hundreds more officers would be needed “to deal with whatever emerges from negotiations about the border in a post-Brexit era”.

He said the PSNI would have to “provide protection for all government agencies working along the 300-mile border and, as such, additional resources will need to be redeployed.”

The PSNI declined to specify the number of new officers it hoped to recruit, where they would be based, or in what capacity but said the plan was being prepared for presentation to British Prime Minister Theresa May’s government.

Britons voted by a 52 to 48 percent margin in June 2016 to leave the EU, although a majority in Northern Ireland voted in favor of remaining in the bloc, seeing open borders as a guarantee of peace and prosperity on the island of Ireland.