Police in Northern Ireland have disputed President Michael D Higgins’ claim that he had to travel to Belfast by private jet because they could not provide security for him to journey by road.
Mr Higgins said his staff were advised "that for security reasons I couldn't be picked up at the border" during last May's trip.
Mr Higgins made his claim about his travel arrangements during a televised presidential debate on Wednesday evening.
"We were advised that for security reasons I couldn't be picked up at the border so the only way of giving the lecture was to go to Belfast [sic]. I'm perfectly happy to drive anytime," Mr Higgins said during the debate.
The PSNI told the BBC: "It is the long-established policy of the PSNI not to comment on the security arrangements made for individuals."
Assistant chief constable Alan Todd added: "The PSNI 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."
In May, Mr Higgins spoke at Queen's University Belfast on the 20th anniversary of the Good Friday Agreement around the concepts of remembering, forgiving, forgetting, and imagining.
Sinn Féin presidential candidate Liadh Ní Riada said Mr Higgins' claim about his transportation had been disputed by the PSNI.
She added: "They reject this security claim [and] say it would be 'inconceivable' that the President of Ireland would not have been afforded security if it had been requested.
"It is clear now that Michael D Higgins' claim has caused considerable anger within the PSNI.
"Michael D Higgins must make a public statement on this matter immediately. This is very serious. He must come clean."
A spokesperson 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."
The spokesperson added: "For logistical reasons and on security advice, the President did use the government plane to travel to Belfast in May, to deliver the Harri Holkeri lecture.
"It would not be appropriate to further comment on the detail of security arrangements."