Theresa May has told her senior ministers she is still confident of reaching a Brexit deal but it must “not be done at any cost” to the UK.
Following the PM’s weekly cabinet meeting, No 10 said the main sticking point remained how to guarantee no new checks on goods at the Irish border.
Downing Street said talks on how to guarantee this had been “constructive”.
The EU’s chief negotiator says there has not yet been enough progress to call a special summit to seal the deal.
Mrs May needs to unite her cabinet behind her position before trying to reach agreement with the EU ahead of the UK’s scheduled departure on 29 March 2019.
Some ministers reportedly want detailed legal advice on what they are signing up to, amid concerns that they could be bounced into accepting a deal.
No 10 said the prime minister assured ministers that the cabinet would meet before the UK agreed to any deal on the terms of the UK’s exit.
The withdrawal deal is said to be 95% complete but the tricky bit is proving to be how to honour the commitment by both sides to guarantee no new hard border in Ireland.
There is disagreement on whether this “backstop” should apply to Northern Ireland, or the whole of the UK – and on whether it should be time-limited or revoked by the UK.
It is understood ministers discussed the mechanism for governing the backstop and who should decide when it no longer applied.
It is an issue because after Brexit it will become the UK’s land border with the rest of the EU, which has a single market and customs union so products do not need to be checked when they pass between member states.
And there have been warnings that a hard border would undermine the peace process in Northern Ireland.
EU negotiator Michel Barnier told a Belgian broadcaster that the Irish border remained the main hurdle to be overcome. If enough progress is made, he said, he will recommend that a summit is convened to finalise the deal.
Meanwhile, the government has published the criteria for allocating scarce permits for British truckers who need to drive in the EU after Brexit.
The permits will be shared out based on: vehicle emissions, number of international journeys in the previous year, number of international journeys as a percentage of all journeys, type of goods transported and an element of chance.
The Department of Transport document says the permits would be required for a no deal scenario BUT might also be required after the future economic partnership is agreed, depending on the type of deal.
Analysis by BBC political editor Laura Kuenssberg
Cabinet is not expected to be where a final decision will be made, even though some people around government would like it to be.
There is real suspicion on the Brexiteer side that the PM will, at some point, try to bounce them into a decision without much discussion beforehand.
But on the other side, some former Remain voices think Theresa May should call the bluff of those who are making it hard.
In a sign that the former Remainers in the Cabinet are starting to present their own pushier front, Chancellor Philip Hammond, the PM’s second-in-command David Lidington and Business Secretary Greg Clark met on Monday night ahead of the get-together.