A homeless man in California. Photograph: Justin Sullivan/Getty Images

A United Nations special investigator who was blocked from visiting the US by the Bush administration has accused the American government of pouring billions of dollars into rescuing banks and big business while treating as "invisible" a deepening homeless crisis.

Raquel Rolnik, the UN special rapporteur for the right to adequate housing, who has just completed a seven-city tour of America, said it was shameful that a country as wealthy as the US was not spending more money on lifting its citizens out of homelessness and substandard, overcrowded housing. 

"The housing crisis is invisible for many in the US," she said. "I learned through this visit that real affordable housing and poverty is something that hasn't been dealt with as an issue. Even if we talk about the financial crisis and government stepping in in order to promote economic recovery, there is no such help for the homeless."

She added: "I think those who are suffering the most in this whole situation are the very poor, the low-income population. The burden is disproportionately on them and it's of course disproportionately on African-Americans, on Latinos and immigrant communities, and on Native Americans."

Rolnik toured Chicago, New York, Washington, Los Angeles and Wilkes-Barre, a Pennsylvania town where this year the first four sheriff sales – public auctions of seized property – in the county included 598 foreclosed properties. She also visited a Native American reservation.

The US government does not tally the numbers but interested organisations say that more than 3 million people were homeless at some point over the past year. The fastest growing segment of the homeless population is families with children, often single parents. On any given night in Los Angeles, about 17,000 parents and children are homeless. Most will be found a place in a shelter but many single men and women are forced to sleep on the streets. 

Los Angeles, which is described as the homeless capital of America, has endured an 18-fold increase in housing foreclosures. Evictions from owned and rented homes have risen about tenfold, with 62,400 people forced out last year in Los Angeles county.

Welfare payments are not enough to meet the rent, let alone food and other necessities. A single person on welfare living in Los Angeles receives $221 (£133) a month – an amount that hasn't changed in a decade. The rent for one room is typically nearly double that. 

Rolnik said that while she saw difficult conditions in all the places she visited, the worst was on the Native American reservation of Pine Ridge in South Dakota.

"You see total hopelessness, despair, very bad conditions. Nothing I have seen in other cities compared to the physical condition of the housing at Pine Ridge. Nothing compared to the overcrowding. They're not visible, they're isolated, they're far away. They're just lost," she said.

Rolnik says that one of the greatest matters of shame is that the US has the resources to provide decent housing for everyone.

"In the US, it's feasible to provide adequate housing for all. You have a lot of money, a lot of dollars available. You have a lot of expertise. This is a perfect setting to really embrace housing as a human right," she said.

Rolnik has given a verbal report to the US state department, which has a month to respond to her observations. She will submit a final written report to the UN human rights council early next year.