Lesotho's foreign minister said on Wednesday he was shocked and insulted by US President Donald Trump saying nobody has heard of the African country, and invited him to come visit.

Trump mentioned Lesotho in his address to US Congress on Tuesday evening while listing some of the foreign spending he had cut as "appalling waste".

"Eight-million dollars to promote LGBTQI+ in the African nation of Lesotho, which nobody has ever heard of," Trump said, drawing laughs in the Congress.

Lesotho's foreign minister, Lejone Mpotjoane, said the remark was "quite insulting".

"I'm really shocked that my country can be referred to like that by the head of state," he told Reuters.

Lesotho, a mountainous nation of about 2-million people that is encircled by South Africa, has the highest base altitude of any country, with its lowest point at 1 400 m and is sometimes called The Kingdom in the Sky.

"Lesotho is such a significant and unique country in the whole world. I would be happy to invite the president, as well as the rest of the world to come to Lesotho," said Mpotjoane.

He said some civil society organisations funded by the US Embassy in Lesotho did work to support the LGBT+ community, but the United States also provided important funding for the country's health and agriculture sectors.

Trump's administration has cut billions of dollars in foreign aid worldwide as it seeks to align spending with Trump's "America First" policy.

Mpotjoane said Lesotho was feeling the impact as the health sector had been reliant on that aid for some time, but that the government was looking at how to become more self-sufficient.

"The decision by the president to cut the aid... it is (his) prerogative to do that," said Mpotjoane. "We have to accept that. But to refer to my country like that, it is quite unfortunate."