Brexit Secretary David Davis and his negotiating team are demanding officials in Brussels produce legal clarification regarding the amount of money it is demanding the United Kingdom hand over on its way out of the 28-nation bloc, the Guardian reports.
The divorce bill has become a major sticking point in negotiations between Britain and the EU.
"The talks this week are technical, before we move on to more substantive talks in September".
It was hoping the papers would persuade the European Union that talks about the future relationship should be brought forward, arguing that divorce issues such as the Irish border will be easier to settle once the terms of a trade deal are clear.
Davis's team have been stung by suggestions the government should have published a paper setting out its own position on the withdrawal bill - pointing out that the commission has not yet produced a paper on the border in Northern Ireland, while Britain has done so.
The third round started badly, with negotiators on both sides barely able to hide their frustration.
Davis said on Monday that he wanted to see "flexibility and imagination on both sides" in negotiations, but the European Union will not move onto discussions of the future relationship until the three key issues have been tackled. European lawmakers will have to approve any separation agreement at the end of the Brexit negotiations.
Like the Conservatives and much of the country, Labour is split over Brexit, and by offering this kind of proposal has opened the way for different factions to put forward their views of how Britain should leave the EU.
His comments came after Brussels" chief Brexit negotiator Michel Barnier said he was concerned about the lack of clarity and insisted "we must start negotiating seriously'.
European Union chief executive Jean-Claude Juncker blasted Britain's failure to answer "huge numbers of questions" on its Brexit plans as negotiators held a new round of talks on a divorce due in less than two years.
"Our desire is to discuss both at the same time: we've repeatedly said that, and that's what we're working towards", said a spokeswoman for the prime minister.
Dieter Kempf said that there doesn't appear to be a single agreed British government position.
He stressed: "The EU will not step back one millimetre from its position in defence of the rights of European citizens".