Campaigning in the early election she has called for next month, May warned voters that the 27 other EU countries were determined to win a divorce deal that "works for them", saying Britain must unite behind her to strengthen her hand.
"These negotiations will not be easy," she told supporters in the eastern part of the city of Bristol, where voters elected a Labour lawmaker in the last election in 2015.
"There are 27 European member states united in their determination to get the deal that works for them. We must show the same unity of purpose here at home to ensure that we get a deal that works in our national interests, too."
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EU leaders take firm stance on Brexit
After meeting May at her Downing Street residence last Wednesday, European Commission President Jean-Claude Juncker was reported to have said he was "10 times more skeptical than I was before" about the possibility of sealing a deal.
May has dismissed the report as "Brussels gossip" and, in an interview with the BBC, suggested she would not be a pushover.
"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.
The prime minister is confident she can make a success of Brexit, her spokesman told reporters, and was approaching the talks "in a constructive manner and with huge amounts of goodwill".
Addressing questions about May's capacity to conduct the time-consuming negotiations, he added: "The prime minister is leading the Brexit talks. She will be assisted by the secretary of state for exiting the European Union and senior officials."
The prime minister, appointed shortly after Britain voted to leave the EU last year, has stuck to her policy of revealing little about her negotiating hand before the talks start - most likely after the election.
She has been accused by opposition lawmakers of taking a high-handed approach towards the rest of the EU in the run-up to the talks, potentially poisoning the atmosphere as battle lines are drawn.
