Raquel Rolnik, the UN special rapporteur on housing, said she had been very shocked by evidence she gathered while on a fact-finding mission to the UK, which included a visit to Edinburgh.
Some tenants were contemplating suicide due to the changes, she warned, adding that the policy could constitute a breach of human rights laws. Many people were increasingly having to choose between food and paying the penalty, she added.
But her criticism has been rejected by the Conservative half of the Coalition, which accused her of not speaking to ministers about the policy.
Tory chairman Grant Shapps has written to UN Secretary General Ban Ki Moon demanding an apology and explanation for what he described as disgraceful comments.
At Westminster, Mr Moore sidestepped the issue of the UN envoy's report and refused to be drawn on a question by SNP MP Angus Robertson on whether the bedroom tax was a "benefit of the Union".
The Scottish Secretary said the Coalition was attempting to tackle an escalating welfare bill in "very tight financial circumstances" while addressing "the mismatch for different families in different accommodation." But he added: "We need to look very carefully at the implementation of that and that's what we are doing."
The LibDems successfully argued for millions of pounds of extra money to be made available earlier this year to help minimise the negative effects of the policy.
Ms Rolnik has defended her report, saying that her visit to the UK had been on the invitation of the Coalition. She also said that she had met with both housing minister Don Foster and Communities Secretary Eric Pickles while in the UK.
At a press conference yesterday she said: "The right to housing is not about a roof anywhere, at any cost, without any social ties. It is not about reshuffling people according to a snapshot of the number of bedrooms at a given night. It is about enabling environments for people to maintain their family and community bonds, their local schools, work places and health services allowing them to exercise other rights, like education, work, food and health."