Ms Patel defended the scheme at a meeting in Geneva with UNHCR chief Filippo Grandi, Rwanda’s Foreign Minister Vincent Biruta and other diplomats, insisting she was trying to save lives by deterring dangerous English Channel crossings.
But Mr Grandi, who said his agency was proposing “concrete alternatives” to Ms Patel, did not back down on his criticism of a plan which he and some activists consider a potential breach of international refugee law.
“Shifting asylum responsibilities is not the solution,” he said after the talks ended with no sign of the two sides seeing eye-to-eye.
Ms Patel, who overruled concerns from her department’s top official to announce the Rwanda plan last month, promised to work with UN agencies but maintained that the deportations would not break human rights laws.
The partnership with Rwanda would "deter criminality, exploitation and abuse, while supporting the humane and respectful treatment of refugees”, she said after briefing US, Australian, Canadian and New Zealand officials on the deal.
Thousands of people have crossed the English Channel in small boats already this year, posing a political and logistical headache to UK ministers. Britain and France have previously blamed each other for failing to stop the people-smuggling trade.
Rwanda last month signed up to the arrangement after being offered £120 million ($150m) in development assistance and funding to provide accommodation for the incoming refugees. Britain and Rwanda have played down concerns about the African nation's human rights record.
Mr Biruta said UNHCR was entitled to its views but Rwanda had “no reason to doubt our motivations or our ability to offer sanctuary” because 130,000 people already take shelter in the country.
The African country has a “long history of offering those in need safety, dignity, and protection”, he said, citing a recent UNHCR-run evacuation from Libya to Rwanda.
Campaigners revealed this week that they had been told the Rwanda flights would not begin until June 6 at the earliest, after Prime Minister Boris Johnson said dozens of people had already been selected for deportation.
Asylum seekers still in Britain are to be housed at a reception centre in Linton-on-Ouse, nicknamed the “Yorkshire Guantanamo” by campaigners in reference to the US detention camp.
The Home Office revealed late on Thursday that Ms Patel planned to visit the village to hear objections from residents that a former Royal Air Force base will be turned into an asylum centre.
“The villagers are in crisis and I mean crisis right now,” local resident Aundrea Watson said at a two-hour consultation with civil servants in Linton.
She accused officials of “not taking on board” that the 1,500 asylum seekers expected to live at the camp would dwarf the village’s population of 300, making her feel unsafe.
“I don’t think you are grasping the concept of what you are doing to our community,” she said.
But Deputy Prime Minister Dominic Raab came to Ms Patel’s defence on Friday, telling BBC Radio 4’s Today programme that refugees were being encouraged to use legal routes to the UK.
He cited the “big-hearted welcome” offered to refugees from Hong Kong, Afghanistan and Ukraine as evidence that Britain was not turning its back on people fleeing persecution.
Tony Smith, a former head of the UK Border Force, told the same programme that "the jury's still out" on whether the Rwanda plan would really deter migrants if they are desperate to reach Europe.
But he sympathised with ministers on the grounds that it was hard to return people to their countries of origin, while reaching consensus with the European Union has proved difficult.
"Migrants know that they really simply need to get into UK territorial waters and they're into the UK pretty well permanently," Mr Smith said. "That's the business model that the government is trying to break."