It will be extremely challenging to give effect to the commitments made by the British government on the future of the border, according to one of the Irish Government's lead Brexit negotiators.

A breakthrough on the status of the border allowed the UK and the European Union to strike a deal last month to pave the way for talks on future trade ties after the UK leaves the bloc in 2019.

The agreement said that, if Britain cannot strike the kind of free trade deal it wishes, Northern Ireland would remain aligned with the rules of the EU single market and customs union, both of which the British government is committed to leaving.

But it also includes a clause that no new regulatory barriers would develop between Northern Ireland and the rest of the UK.

"The British government has made a series of very welcome and important commitments. But of course giving effect to those commitments will be extremely challenging", said Rory Montgomery, Second Secretary General at the Department of Foreign Affairs, in a speech in Dublin.

"One of the key questions ... is to what extent will it be possible for it to enshrine, if you like, the commitments and protections agreed before Christmas.

And of course how will this sit with the other set of commitments made by the British government to the DUP and Northern Ireland," he said. "That will be a major challenge".