After the meeting at her Downing Street residence, European Commission President Jean-Claude Juncker was reported to have said he was "10 times more sceptical than I was before" about the possibility of sealing a deal on EU divorce terms for Britain and a new trading relationship.
May, who took over as Conservative Party leader and prime minister shortly after the Brexit vote last year, is calling on voters to back her at a June 8 election in order to strengthen her hand in upcoming negotiations.
Asked during an interview with the BBC whether, given the noises coming out of Brussels, she thought her approach to Brexit was realistic, May said: "What we've seen recently is that at times these negotiations are going to be tough."
"During the Conservative Party leadership campaign I was described by one of my colleagues as a bloody difficult woman. And I said at the time the next person to find that out will be Jean-Claude Juncker," she said.
May dismissed the account that was given to the Frankfurter Allgemeine newspaper of the meeting as "Brussels gossip".
The newspaper report also said May had proposed to Juncker that Britain and the EU could agree a deal on the future of EU nationals in Britain and Britons in the EU at a June summit but that he had made it clear there were too many legal complexities to resolve the issue so quickly.
Asked by the BBC whether reaching an agreement in June was feasible, May said: "I've always said that there are complexities to this issue and lots of details that will need to be agreed.
"What people want to know is to have some reassurance about their future. I believe we can give that at an early stage. I've got the will to do this," she added.
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