Government tensions are running high over the precise wording of a "backstop" deal on customs to prevent the imposition of a "hard border" on the island of Ireland.
The issue of the border between Northern Ireland and Ireland is one of the last remaining obstacles to achieving a divorce deal, with wrangling continuing over the nature of a "backstop" to keep the frontier open if a wider UK-EU trade arrangement can not resolve it.
A British government spokesman said progress had been made in some key areas.
The government statement suggests the Northern Irish backstop is not the only outstanding issue.
Theresa May is under pressure to reverse course after Cabinet ministers threatened to walk out over her reported plans for a potential Brexit "backstop" which could effectively keep Britain permanently inside a Customs Union with the EU after Brexit.
Former Cabinet colleague David Davis openly threatened Mrs May with a leadership election unless she changes her stance on Brexit, while up to nine Cabinet ministers are considering resigning over the issue.
Tory MP Nadine Dorries suggested that Mr Davis should be installed as interim leader, claiming that was the only way to secure the kind of free-trade deal Brexit demanded by Eurosceptics.
In a strongly-worded article in the Belfast Telegraph, Mrs Foster warned against the EU's backstop proposal and also stressed that she would not accept any measure that resulted in extra checks for goods travelling between Great Britain and Northern Ireland.
Mrs May's counter-proposal is for a "temporary customs arrangement" for the whole United Kingdom, but Tory Brexiteers are suspicious this could turn into a permanent situation, restricting the freedom to strike trade deals around the world.
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So even if May strikes a deal with Brussels, she will struggle to get it past her government and Parliament at home.
But Health Secretary Matt Hancock urged ministers to unite behind the prime minister, insisting there were "different ways" to ensure any customs commitments were "credibly time-limited".
Not for the first time, the Democratic Unionist party is threatening to torpedo her plans to secure a Brexit deal with the European Union but this time it coincides with open revolt from inside her cabinet, a combination that could prove lethal to the prime minister. However, we do not want nor need the regrets of another prime minister.
Speculation about possible resignations has centred on Andrea Leadsom, Penny Mordaunt and Esther McVey, but the newspaper also indicated that Scottish Secretary David Mundell and Scottish Tory leader Ruth Davidson could quit because special arrangements for Northern Ireland could fuel the case for Scottish independence.
A total of 44 letters demanding a vote were reportedly submitted to the Conservative 1922 Committee - just four short of the number required to trigger a ballot.
Critics of the Prime Minister believe the threshold could be passed by Wednesday, depending on the nature of her approach to the Brexit talks.
Someone who has looked into this so you don't have to is Lars Karlsson, the former Director of the World Customs Organisation, who was asked to investigate solutions by the European Parliament - hardly a pro-Brexit organisation!
Trade secretary Liam Fox told friends that her proposal "would make life very hard for me", according to a Mail report, because it would limit the UK's ability to strike new free trade deals outside the EU.