Officials from the teams of British Brexit Secretary David Davis (left) and EU chief Brexit negotiator Michel Barnier are feverishly trying to put finishing touches on a deal ahead of the December 15 summit. | Emmanuel Dunand/AFP via Getty Images EU holds hard line as Brexit talks enter frenzied weekend Points on the financial settlement, citizens’ rights and the Northern Irish border are still being negotiated.

It's not just Ireland.

While Brexit negotiators working frantically behind closed doors were focused heavily Friday on the vexing questions around the Ireland-Northern Ireland border, EU diplomats said that other stumbling blocks remained. Despite the U.K.'s increased offer on the Brexit bill, an array of crucial details on the financial settlement remain to be worked out, and the issue of European Court of Justice jurisdiction over citizens' rights disputes is also not resolved.

As officials braced for a weekend of intense negotiations, ahead of what's billed as a make-or-break lunch on Monday between Prime Minister Theresa May and Commission President Jean-Claude Juncker, EU diplomats said the bloc remained resolute in its demand for "sufficient progress" on all three key divorce issues before allowing talks to proceed to discussion of a transition period and the framework of a future trading relationship.

"It's too early to lower the bar," one EU diplomat said. "Negotiations are still ongoing."

At the same time, diplomats said the delicate politics surrounding any agreement — particularly on the Ireland question — could combust at any moment, potentially obliterating hopes of a deal before the European Council summit two weeks hence.

"On the political capacity to wrap things up, it is uncertain," a senior EU diplomat said.

Lunch for two

For their part, the British are already looking to push Monday's "absolute deadline," as laid down by European Council President Donald Tusk as the final point at which summit conclusions could be prepared in time. “We have always said we are working towards the European Council, which is December 14,” May’s spokesman James Slack told reporters Friday.

While May at the lunch on Monday is expected to present an expanded offer on the so-called single financial settlement, diplomats and officials in the EU27 capitals said they had still not seen the details, leaving many to wonder if the offer would be sufficient to win unanimous endorsement.

"A part of the Commission, as well as the French and the Germans have the toughest position" regarding the U.K.'s financial settlement, said a Hungarian diplomat in Budapest, who spoke on condition of anonymity. "But we think that most of the members now see the financial settlement as acceptable, and our judgement is that the Commission is leaning that way as well," this person said, adding that all member countries will end up agreeing the U.K.'s offer.

Another EU diplomat suggested that some countries are hiding behind France and Germany. “I would not describe necessarily France and Germany as the hardliners," the diplomat said. “They probably play more hardball on the role of the [European Court of Justice] but there have always been differences among the 27, there’s always been a divergence of opinions, nothing dramatic though,” the diplomat said.

However tough the line from the EU27, the lengths Britain is willing to go to meet the financial obligations is a question with potentially billions of euros in consequences for the EU27, who would be left to shore up the EU budget or make drastic cuts to programs.

Sweden's EU and trade minister Ann Linde had encouraging words for the U.K. Friday on the prospects of achieving the sort of enhanced trade deal it wants, but she was adamant about the Brexit bill. Just covering the existing budget cycle was not enough, she said. "What we want is that decisions that have been taken, for example on the pensions of civil servants, or promises we have made to Ukraine, or issues like development cooperation — all these things that we have decided as 28 — should be honored,” Linde said. “That’s what we are talking about. Not just the two years left in the budget.”

“It’s complicated work because every word counts," one EU diplomat said. "We are getting there now ... What we understand is that Barnier is now ticking all the boxes, and we are close to a deal.”

Irish conundrum

By far the most complicated issue remains how to avoid the reimposition of a hard border between Ireland and Northern Ireland once the U.K. leaves the EU's single market and customs union. Ireland's Deputy Prime Minister Simon Coveney has said that his country will veto the move to phase two if it is not satisfied with the results of the phase one negotiations, even though Dublin does not want to be portrayed as single-handedly standing in the way of a deal.

"It is up to Ireland to assess whether there is sufficient progress," said the same diplomat.

As a show of unity, European Council President Donald Tusk will meet Irish Prime Minister Leo Varadkar Friday evening.

Ahead of that meeting Coveney reiterated that Ireland would not be pushed into agreeing to sufficient progress. “We cannot just move to phase two discussions in the hope that this can be resolved,” he said Friday according to the Guardian. “We can work through this. We want to listen to unionism. They are of equal importance but at the same time, we can’t allow one party to dictate what is acceptable and what is not.”

But he expressed optimism that a deal can be done on the border issues. “I think it is doable ... We are not where we need to be today, but I think it is possible to get to be where we need to be in the next few days,” he said.

Several officials cautioned that open questions remained even on citizens' rights — the area widely considered to be closest to "sufficient progress." In particular, they said there were open points of negotiation about family reunification, including the rights of children not yet born to citizens who will retain residency rights in the U.K. or EU. The question of what jurisdiction the European Court of Justice will have in the U.K. post-Brexit is also still not solved.

The U.K. has long insisted that it does not want to subject to the court's rulings after Brexit, while Brussels has been equally adamant that the court must retain a role in adjudicating any disputes over citizens' rights.