The leader of the Northern Ireland Greens has warned that a physical border on Ireland following Brexit "will increase the likelihood of violence".
Steven Agnew MLA compared a "mythical" technical solution to a unicorn, and said the only way forward is to remain in the single market and customs union.
Speaking at the Scottish Greens spring conference in Greenock, Inverclyde, he outlined what he believes are the three options regarding the border - leaving the customs union and having a land border, doing the same and have a sea border or remaining in the single market and customs union.
He said: "Just like the unicorn, the so-called technical solution to the border in Ireland is a mythical creature.
"It exists only in Brexiteers' imaginations."
He added: "As Greens we can see that arguing which border is worse is arguing between the frying pan and the fire.
"Either way our economy in Northern Ireland is going to be damaged, either way it will see job losses, either way it will see businesses going to the wall.
"What I want to see in Northern Ireland, and what the Green Party is pushing for, is a political convergence to say that, no, we as Northern Ireland and the whole of the UK must stay in the customs union and ensure no hard border is a meaningful phrase."
He said it is "utterly irresponsible" of the UK Government to place the Irish peace process at risk.
He added: "It is naive to think that in the short 20 years since the Good Friday Agreement that we have cemented the peace to such an extent that we can now start to unravel the agreement that secured it.
"I've no doubt that if there is a a physical border on the island of Ireland, any type of infrastructure, that it will increase the likelihood of violence."
He said if the UK does not remain in the customs union and the single market, "the term no hard border just becomes another Brexit lie".