"An orderly withdrawal of the United Kingdom from the Union requires settling the financial obligations undertaken before the withdrawal date," said the European Commission document seen by AFP Thursday.
"The agreement should define the precise way in which these obligations will be calculated... the obligations should be defined in euro," it added.
The document did not say how much the Brexit settlement might cost but EU officials have previously said it could be as much as 60 billion euros, sparking howls of outrage in London, which puts the figure nearer 20 billion.
Titled "Non Paper on key elements likely to feature in the draft negotiating directives," the document was drawn up for the European Commission, which will conduct the Brexit negotiations with Britain.
It covers in more detail the same ground outlined last month by EU president Donald Tusk in response to Prime Minister Theresa May's official March 29 notification that Britain was leaving the bloc.
Tusk stressed then that the EU will insist on agreeing the future of citizens in Britain and the Brexit bill first before considering London's demand for a free trade pact.
The Commission document outlined its aims for a reciprocal deal for EU citizens in the UK and Brits elsewhere in the bloc, saying their rights should last "for the lifetime of those concerned" rather than giving a cut-off date.
The Brexit divorce settlement should not just be limited to workers, the paper said, and should also apply to family members who join citizens "at any point in time before/after the withdrawal date".
Residency and social security were also highlighted by the Commission as rights it will seek to protect in the two-year negotiations with London, as the two sides try to undo the mass of legislation agreed since Britain joined then European Economic Community in 1973.
Both the divorce bill and the fate of EU citizens are expected to be among the toughest areas to reach agreement on, following a Brexit campaign that rallied against Britain's payments to Brussels and the number of migrants in the country.
Anticipating possible disputes, the draft paper envisaged setting up "an institutional structure to ensure an effective enforcement of the commitments under the agreement," while maintaining the primacy of the European Court of Justice.
For disputes outside EU law, "an alternative dispute settlement should only be envisaged if it offers equivalent guarantees of independence and impartiality as the ECJ," it added.
On a visit to London on Thursday, the head of the European parliament, Antonio Tajani, said that after Brexit, EU citizens living in the UK should have the "same rights as today".
"For us it's important to ensure that Brexit does not have any negative effects on their life and the rights they are enjoying," he said, stressing that "it is a priority and it is a red line".
Tajani, who also met with Prime Minister Theresa May during his visit, said Britain could still change its mind on Brexit.
"If the UK wanted to stay, everybody would be in favour. I would be very happy," he said.
May, who called for snap elections for June 8 seeking to increase her slim majority before gruelling negotiations with Brussels, has said several times that there could be "no turning back" on Brexit.
(Except for the headline, this story has not been edited by NDTV staff and is published from a syndicated feed.)