The imposition of border controls between Britain and the island of Ireland has not been ruled out by the UK's Brexit Secretary David Davis.
Mr Davis told MPs he did not see such a move as the solution to concerns over a possible post-Brexit "hard border" between Northern Ireland and the Republic, but stopped short of killing off the idea.
Giving evidence to the Commons Exiting the EU Committee, the Minister was asked to specifically rule out Irish Sea border controls by the DUP's Sammy Wilson.
Mr Davis replied: "I don't know, Mr Wilson, at the moment. My view here is, I don't see that would be the solution, to be honest.
"The primary concern for me, the reason I'm hesitating, is the primary concern for me is to make sure that we don't have that hard border. And there are various technical ways of resolving that.
"We haven't finished that process, we are doing it in consultation with the Irish government, or we are making progress with the Irish government. We may not have a solution to it in the next few months.
"I can see the issue, absolutely see the issue, and I can see why that's a very second best solution. I think we can find a better one, but I won't make a promise today."
Earlier in the exchanges, Mr Davis said he was "optimistic" about maintaining an open border between Northern Ireland and the Republic following the UK's withdrawal from the EU.
But he said he did not envisage a special arrangement which might keep Northern Ireland inside the EU's Customs Union, as part of the Brexit deal.
Mr Davis told MPs the Government was "determined" to keep an open border, with no fences and no checkpoints, dismissing suggestions that this would create a route into the UK for people trying to evade post-Brexit immigration controls.
He said the European Commission's chief Brexit negotiator Michel Barnier and the Dublin government shared this goal, making an agreement likely.
One possible model for the future border was the very lightly-controlled border between Norway - which is outside the EU and the European Customs Union but part of the Single Market - and EU member Sweden, he told the cross-party committee.
Mr Davis said the open border allowing easy passage of people and goods between the Republic and the North was "a very important part" of the peace agreement to end the Troubles in Northern Ireland.
He added: "We are determined to maintain that as an open border.
"I am optimistic that the EU will be helpful to us on this. Michel Barnier is also very seized of this. When I saw him, we didn't talk about the negotiation but he did raise out of nowhere his involvement in it and his commitment to it. It gave me a degree of comfort that we should be able to do this in some way."
He added: "When I went to Dublin, they were equally keen to maintain this. We may have discussions with them about their own incoming security, so we have got at least some watch-list there, but that's for them to decide, not me."
The UK and Irish Common Travel Area was already recognised in the EU's Amsterdam Treaty, he pointed out.
The prospect of people using the Irish route to get in the UK was "not a big issue", he said, adding: "People say 'Won't Ireland be a route into Britain?' There are 50 million people landing at British airports every year. It's a very long-winded way to get into the UK to come via Dublin.
"If you want to get in, you come as a tourist and stay. That's what happens. I don't see a circumstance where we are going to stop tourists at all. We are going to have loads of people coming in and out of Britain."