The inconclusive elections in Britain have further complicated matters.
Brexit talks will begin Monday.
The Democratic Unionist Party wants to attach its own conditions onto Brexit as part of its deal with the Conservatives - including the insistence on a "soft border" between Northern Ireland and the Irish Republic. The price of such a deal remains unclear.
May is not expected to announce an agreement with the DUP until next week.
Monday will just be the first day of what will be more than 18 months of talks.
But the Government will press ahead with the first round of Brexit talks two days before the official opening of Parliament. Hundreds of protesters chanting "we want justice" stormed a local town hall on Friday afternoon.
It had been suggested the start of negotiations could be delayed by the failure of any party to win a House of Commons majority at last week's General Election.
The DUP is one of the most socially conservative parties in Europe, having sought to maintain some of its strictest limits on abortion and consistently opposed gay marriage.
But her vulnerability at home means that her plan to leave the EU's lucrative single market and customs union in order to impose strict limits on immigration is under intense scrutiny.
Prime Minister Theresa May invoked Article 50 of the Lisbon Treaty, which started the clock on Brexit, in March.
May's finance minister, Philip Hammond, said on Friday that Britain should prioritise protecting jobs and economic growth. "We'll see about the rest", Merkel told reporters after a meeting with top government officials, unions and business leaders in Meseberg, a town in eastern Germany.
A senior Brussels official said the amount, which compares to London's annual net European Union payment of around 10 billion euros, would still be "peanuts" in terms of the overall economy and also that the final bill would be determined less by technical and legal arguments than by hard-headed political horse-trading.
"Our view is that withdrawal agreement and terms of the future relationship must be agreed alongside each other", said the spokesman.
"I'm not going to give a blow by blow account of how we propose to take that discussion forward", he said.
The Brexit Department said in a statement that the U.K.'s withdrawal and future ties are "intimately linked".