The Republic has no agreement with the British government about the use of Irish ports following Brexit, Taoiseach Enda Kenny has said.
“We do not know yet what the British government is actually looking for here,’’ he said.
“Is it a hard Brexit exit from the customs’ union and the single market and control at their own borders, or is it something else ?’’
Mr Kenny told the Dáil on Wednesday Ireland would remain an EU member.
"If, for instance, the UK removed itself from the customs' union, that is going to lead to a serious challenge in terms of tariffs from the World Trade Organisation, '' he added.
There would also be a challenge if the UK removed itself from the single market, and try to control its own borders, he said.
Mr Kenny said he had made it clear, following his meeting with the British prime minister in Downing Street, that the Irish Government did not want a return to a hard border and an end to the common travel area.
Ireland, he said, did not want to see a return to the traditional customs’ posts, which had led to all sorts of incidents such as smuggling and more serious matters of life and death.
The Taoiseach was replying to Sinn Féin leader Gerry Adams, who asked whether agreement had been reached with the British government that immigration controls would be put in place at Irish ports and airports.
He said it was his fourth attempt to get the Taoiseach answer the question.
Mr Adams said such controls would not be viable.