Ireland's Taoiseach Leo Varadkar outside 10 Downing Street | Carl Court/Getty Images | Carl Court/Getty Images Irish PM: EU prepared to wait for Brexit ‘concessions’ Dublin opposes talks on trade until London provides assurances about a post-Brexit border with Northern Ireland.

GOTHENBURG, Sweden — The EU is willing to wait for "concessions" on Brexit, even if that means continuing Phase 1 of talks into next year, Irish Taoiseach Leo Varadkar said Friday.

Varadkar, arriving in Gothenburg for an EU summit on social rights, said Ireland opposed starting talks on a future trade relationship with Britain until London provided written assurances about the post-Brexit border between Northern Ireland and Ireland.

"The U.K. voted 18 months ago to leave the European Union. That's a sovereign decision of the British people — we respect it," Varadkar said, before heading into a bilateral meeting in Gothenburg with U.K. Prime Minister Theresa May. "But the British government went further," Varadkar said.

"The British government decided that the U.K. would leave the customs union, they would leave the single market, they have taken that off the table before we even talk about trade," he continued. "What we want to take off the table before we even talk about trade is any idea that there would be a hard border, physical border or a border resembling the past in Ireland."

Varadkar said he remained optimistic "sufficient progress" could be made by the December EU leaders' summit in Brussels, but that the EU was prepared to wait for "concessions" and that it sometimes seemed the U.K. was not sufficiently prepared for the entire Brexit process.

"It is certainly possible that we can come to conclusions in December allowing Phase 2 talks to begin," Varadkar said. "But, you know, if we have to wait until the new year, or if we have to wait for further concessions, so be it. What I think would be in our all of our interests is that we proceed to Phase 2 if we can in December. It's 18 months since the referendum, it's 10 years since people wanted a referendum, started agitating for one. Sometimes it doesn't seem like they thought all of this through."

Varadkar said having a written agreement with assurances on the Irish border and sufficient progress on the financial settlement and citizens' rights were essential for completing Phase 1.

"We have been talking 18 months, we have been given assurances now for 18 months since the referendum that there will be no hard border in Ireland, that there won't be any physical infrastructure, that we won't go back to the borders of the past and we want that written down in practical terms in the conclusions of Phase 1," he said. "We have put out a mechanism by which that can be achieved. "

May arrived at the summit moments before Varadkar, passing briskly along the blue carpet in front of reporters and camera crews gathered to greet the leaders. May greeted Swedish Prime Minister Stefan Löfven, the summit's co-host, with a handshake and briefly posed for pictures with him.

Brexit is not on the agenda of the social summit, but with the talks now in a crucial phase, the U.K.’s withdrawal will be discussed on the sidelines. In addition to her meeting with Varadkar, May was scheduled to talk about Brexit with European Council President Donald Tusk.