The EU's chief Brexit negotiator says the future of the Irish border is up for discussion in talks today.
Michel Barnier was speaking as he welcomed the UK's Brexit secretary David Davis to Brussels.
They are beginning the second phase of Brexit talks after they officially got underway last month.
Speaking to reporters ahead of those talks, Mr Barnier mentioned the role of Ireland would be specifically discussed.
"Our negotiating groups will work on citizens' rights, on the financial settlement, and other separation issues," he said.
"Our co-ordinators will engage in a political dialogue on Ireland."
Brexit Secretary David Davis has said talks on the "substance" of EU withdrawal are now under way as a fresh round of negotiations began in Brussels.
Mr Davis said: "We are now getting into the substance of the matter.
"It's four categories really. The issue of citizens' rights, the issue of finance, the issue of separation issues and, of course, separately, Northern Ireland.
"For us it's incredibly important we now make good progress. That we negotiate through this and identify the differences, so that we can deal with them, and identify the similarities so that we can move forward.
"And now it's time to get down to work and make this a successful negotiation."
The talks are taking place against a backdrop of increasingly bitter and public feuding among UK ministers over the Government's Brexit strategy.
Over the weekend, Chancellor Philip Hammond angrily accused Cabinet rivals of trying to undermine his agenda for a "softer" business-friendly Brexit prioritising jobs and the economy.
One unnamed Cabinet minister was reported to have hit back, claiming Mr Hammond was part of an attempt by "the Establishment" to prevent Britain ever leaving the EU.
The Daily Telegraph quoted the minister as saying: "What's really going on is that the Establishment, the Treasury, is trying to f*** it up. They want to frustrate Brexit."