Chief EU Brexit negotiator Michel Barnier has responded to claims from Arlene Foster that he does not understand unionist culture.
Speaking at the beginning of a two-day visit to Ireland, Mr Barnier said he did not want to engage in "polemics" with the DUP leader.
He said "my door is open" to the DUP after Ms Foster said Mr Barnier would not be hearing any pro-Brexit voices today.
NEWS: EU Chief Negotiator Michel Barnier says we have no choice but to protect the Good Friday Agreement pic.twitter.com/DCIZnl3Xdw — LMFM RADIO (@LMFMRADIO) April 30, 2018
Mr Barnier urged rapid agreement by June on the scope of any British alignment with the single market that would prevent a hard border post-Brexit.
He said there should be "safety controls" to protect the European trading bloc.
A backstop option for the EU withdrawal agreement would see continued Northern Ireland alignment with EU rules affecting the all-island economy, but any divergence from the rest of the UK would meet strong unionist objections.
Mr Barnier said: "We need to agree rapidly by June the scope of alignment, what I call the safety controls that are ... to respect the single market."
He added: "We want to succeed with the UK, not against the UK.
.@simoncoveney tells #aicd he believes the Irish govt can trust @MichelBarnier. “He is on our corner until the end of the process” SC says pic.twitter.com/bMcCFsYvit
— Tracey Magee (@Tracey_utv) April 30, 2018
"Together with the Irish government we are looking for practical solutions."
On Monday Mr Barnier delivers a keynote speech during a meeting of the Dublin government-hosted All-Island Civic Dialogue on Brexit in the border town of Dundalk, Co Louth.
He then crosses the frontier to Newry in Co Down for meetings with business leaders.
On Tuesday Mr Barnier will visit the other, north-western end of the border at Derry.
It will be the UK's only land border with an EU country after Brexit and is among the most vexed issues facing negotiators.
It is his third visit to the Republic and Tánaiste and foreign affairs minister Simon Coveney said he was a friend to Ireland.
Earlier, DUP leader Arlene Foster told the BBC: "He's hearing a very strong message from the Republic of Ireland's government, he's hearing it from Sinn Féin.
"We have tried to get him to understand the unionist position for the people of Northern Ireland, but he hasn't really responded to that and I'm disappointed about that.
"I am also disappointed that he will hear anti-Brexit voices tomorrow, he won't hear any pro-Brexit voices tomorrow because he is being taken around by Sinn Féin MPs."
A joint report on the UK's withdrawal agreed in December by British Prime Minister Theresa May and European Commission president Jean-Claude Juncker included both British proposals, along with a third "backstop" option which would keep Northern Ireland in the customs union.
But a version published by the EU in February and agreed by the EU27 last month contained only the "backstop", effectively drawing a customs border down the Irish Sea, which a furious Mrs May said "no British prime minister could ever agree".
Mr Barnier has said that substantial parts of the withdrawal deal - including a solution for the border - remain to be agreed by the autumn.
