The PSNI have rejected a claim by the Irish president that he had to travel to Belfast by private jet earlier this year because they could not provide security for him to travel by road.
Michael D Higgins said his staff were advised “that for security reasons I couldn’t be picked up at the border”.
His car was driven from Dublin to Belfast to pick him up at the airport.
Mr Higgins’ spokesman told BBC News NI that “for logistical reasons and on security advice”, a jet was used.
Well-placed PSNI sources have rejected the security claim.
The president travelled to Belfast in May.
“It would be inconceivable that the President of Ireland would not have been afforded security if it had been requested,” a PSNI source told the BBC.
Another source said there is anger within the PSNI at the suggestion that it did not have sufficient resources to escort Mr Higgins from the border to Belfast.
The president made the claim during a televised presidential debate on Wednesday night.
A spokesman for Mr Higgins said: “The president has made many visits to Northern Ireland by car and is grateful for the support received from the security services.
“For logistical reasons and on security advice, the president did use the government plane to Belfast in May, to deliver the Harri Holkeri lecture.
“It would not be appropriate to further comment on the detail of security arrangements.”
Mr Higgins is seeking a second term in office. The election takes place on 26 October.
He travelled to Queen’s University to speak at an event organised by the Senator George J Mitchell Institute for Global Peace, Security and Justice in May.
In a statement, the PSNI said: “It is the long established policy of the Police Service of Northern Ireland not to comment on the security arrangements made for individuals.”
“The Police Service of Northern Ireland routinely work with visiting heads of state and other key figures visiting Northern Ireland and make full provisions for their safety in line with their requirements,” Assistant Chief Constable Alan Todd added.
The clear inference is that the PSNI would have provided security for the president’s visit to Belfast in May if asked to do so.
“No matter how busy we were with other duties, the fact that there are more than 6,500 PSNI officers means we would have had the necessary resources to provide an escort if we had been asked,” said a source.