The United Nations has condemned US president Donald Trump's reported description of African nations and Haiti as "s***hole" countries as "shocking and shameful", and "racist".

"If confirmed, these are shocking and shameful comments from the President of the United States. Sorry, but there is no other word one can use but 'racist'," Rupert Colville, spokesman for the UN human rights office, told reporters in Geneva.

He was referring to comments reportedly made by Mr Trump during a meeting on Thursday with members of Congress about immigration reform, demanding to know why the United States should accept citizens from "s***hole" countries.

Hours later, Mr Trump implied he did not use the word “shithole” to describe Haiti and African countries in two tweets, saying "the language used by me at the DACA meeting was tough, but this was not the language used."

The language used by me at the DACA meeting was tough, but this was not the language used. What was really tough was the outlandish proposal made - a big setback for DACA!Never said anything derogatory about Haitians other than Haiti is, obviously, a very poor and troubled country. Never said “take them out.” Made up by Dems. I have a wonderful relationship with Haitians. Probably should record future meetings - unfortunately, no trust!The comments, first reported by The Washington Post, sparked anger among Democrats and Republicans and revived questions about Mr Trump's tendency to make racially charged remarks.

"You cannot dismiss entire countries and continents as 's***holes' whose entire populations, who are not white, are therefore not welcome," Mr Colville said.

He also took issue with Mr Trump's reported suggestion that the United States should welcome immigrants from places like Norway, whose population is overwhelmingly white, instead of from African countries and Haiti.

"The positive comment on Norway makes the underlying sentiment very clear," Mr Colville said.

"Like the earlier comments made vilifying Mexicans and Muslims, the policy proposals targeting entire groups on grounds of nationality or religion, and the reluctance to clearly condemn the anti-Semitic and racist actions of the white supremacists in Charlottesville - all of these go against the universal values the world has been striving so hard to establish since World War Two and the Holocaust," he said.

"This is not just a story about vulgar language. It's about opening the door wider to humanity's worst side, about validating and encouraging racism and xenophobia that will potentially disrupt and destroy the lives of many people.

"This is perhaps the single most damaging and dangerous consequence of this type of comment by a major political figure."

The US ambassador to Panama resigned, according to Reuters news agency, telling the State Department in a letter that he could no longer serve in the Trump administration.

The African Union said it was "frankly alarmed" by Mr Trump's comments.

"Given the historical reality of how many Africans arrived in the United States as slaves, this statement flies in the face of all accepted behaviour and practice," African Union spokeswoman Ebba Kalondo told the Associated Press. "This is particularly surprising as the United States of America remains a global example of how migration gave birth to a nation built on strong values of diversity and opportunity."

In Botswana, the US ambassador was summoned in a letter and asked "to clarify if Botswana is regarded as a 'shithole' country".In response to Mr Trump's suggestion that the US should seek more immigrants from countries like Norway, Torbjoern Saetre, a politician representing Norway’s Conservative Party in a municipality near Oslo tweeted: “On behalf of Norway: Thanks, but no thanks”.