BRUSSELS -- British lawmakers met the European Union's chief Brexit negotiator on Friday, seeking an iron-clad guarantee that the 1.3 million U.K. citizens in the bloc won't have their rights removed and their lives disrupted if Britain leaves the EU without a deal.
The rights of U.K. citizens living in the 27 other EU nations, and those of the more than 3 million EU citizens in Britain, are one of the thorniest issues of the Brexit negotiations.
Their rights to live, work and study are protected under an agreement struck between the two sides -- but the divorce agreement has been rejected by Britain's Parliament, raising the prospect of a no-deal Brexit.
The U.K. is due to leave the bloc on Oct. 31, and both men vying to take over as prime minister next week, Boris Johnson and Jeremy Hunt, say it's imperative that Brexit happens, with or without a deal.
Conservative lawmaker Alberto Costa, who led the cross-party delegation that met EU negotiator Michel Barnier in Brussels, said "if there's no agreement, there's no protection."
"British nationals will potentially lose access to pension entitlement, lose access to health care entitlement, lose access to welfare entitlement and a whole gamut of other issues," he said.
Talks between the British government and the EU on guaranteeing citizens' rights if the U.K. crashes out of the bloc have failed to produce a breakthrough. EU leaders insist the withdrawal agreement can't be chopped into chunks -- Britain must accept all of it or none.
Some EU member states have said they will preserve Britons' rights, but only if the U.K. reciprocates. Britain says all EU citizens living in the country can stay, but has not enshrined that right in law.
"People assume it's fine, everything's dandy . citizens' rights, of course they're going to protect them, that goes without saying," Costa said. "But we have no extraterritorial powers to pass legislation to protect British citizens in the EU. That can only be done with an agreement with the EU."
The winner of the contest to become Britain's next prime minister -- widely expected to be Johnson -- is due to be announced Tuesday.
Costa said whoever wins must ensure citizens' rights are upheld even if there is no Brexit deal.
German Chancellor Angela Merkel on Friday reiterated the EU's long-held stance that it will not renegotiate the divorce agreement it struck with outgoing British Prime Minister Theresa May.
"The withdrawal agreement is the withdrawal agreement," she said.
"I trust very firmly that Britain will find its way," May said in Berlin at her annual summer news conference. "It is a proud, great nation and it will remain our partner even if Britain is no longer a member of the European Union."
The upcoming change in prime minister also had U.S. President Donald Trump sharing opinions on British politics Friday.
Trump enthused about Johnson becoming the U.K.'s next leader when he was asked about the former London mayor and British foreign secretary during a photo op with reporters in the Oval Office.
He said he spoke with Johnson on Thursday and predicted a positive direction for U.S.-U.K. with him occupying 10 Downing Street.
"I like Boris Johnson. I always have. He's a different kind of a guy, but they say I'm a different kind of a guy, too," Trump said. "We get along well. I think we'll have a very good relationship."
Trump also panned outgoing prime minister Theresa May's handling of Brexit, as he had previously.
"I think the previous prime minister has done a very bad job with Brexit. What can I say?" he said. I mean it's a disaster and it shouldn't be that way. I think Boris will straighten it out."
Jill Lawless in London, Eileen Putman in Washington, and Geir Moulson in Berlin contributed to this story.