Ireland's premier Leo Varadkar has said he will not dismiss the idea of building a bridge between Northern Ireland and Scotland, but insisted the UK must pay for it.
UK Prime Minister Boris Johnson and the Democratic Unionist Party have spoken in favour of the idea.
Last week Mr Johnson described it as a "very interesting idea" and added: "Watch this space."
Mr Varadkar revealed he told the UK premier it was "worth examining".
But the Taoiseach said he had also told Mr Johnson he would expect the UK to pay for it.
Mr Varadkar added: "At which point he suggested, 'no, no, the EU is going to pay for it'.
"So that's definitely not going to happen, because neither Northern Ireland or Scotland are going to be in the EU. But it was kind of half serious, half joking in a way.
"But all messing aside, I do think at the very least a high-level engineering assessment should be done as to whether it is a viable proposal."
Two possible routes for a bridge have been floated in the past - from Portpatrick to Larne, or from near Campbeltown to the Antrim coast.
Architect Prof Alan Dunlop previously said the "Celtic bridge" would cost about £15bn, a fraction of the estimate of £120bn for an English Channel bridge.
Other parties have been less enthusiastic about the idea, with Ulster Unionist Party leader Steve Aiken saying investment in Northern Ireland's existing infrastructure was a greater priority.
Mr Varadkar said: "I know people dismiss these things out of hand, but they used to dismiss the Channel Tunnel as well - the idea of building a tunnel between France and Britain - and I know what I see when I see a bridge tunnel between Denmark and Sweden, when you fly over New Orleans and you see 110 miles of bridge, it's extraordinary.
"I think we need to at least check out if this is viable in engineering terms and how much money it would cost to do."
However, Mr Varadkar also said his focus was on improving existing infrastructure, such as a high-speed rail link connecting Dublin, Belfast and Cork.