The EU Commissioner for Taxation and Customs has said EU custom checks on Irish ports and airports may be necessary after Brexit.
Pierre Moscovici says the EU does not want to see a hard border return to Ireland, but does need to protect its customs area.
The Commissioner said it is up to the UK to come up with a Brexit roadmap before his office responds to Irish customs issues.
"Madame May pronounced recently an important speech that needs to be translated in concrete proposals and I cannot offer you a roadmap," he said.
"But the only thing I can say is that we are really watching this question of the border between Ireland and Northern Ireland, that we don't want to backtrack, we don't want to go back to the past."