Saudi's Crown Prince Mohammed bin Salman has brushed off comments from United States President Donald Trump that Washington is "subsidising" the kingdom's military, Bloomberg reported on Friday.

The crown prince insisted that the kingdom has always paid for armaments from the US.

"Ever since the relationship started between Saudi Arabia and the United States of America, we've bought everything with money," he told Bloomberg in an interview.

Last week at a rally Trump asked, "when you have wealthy countries like Saudi Arabia, like Japan, like South Korea, why are we subsidising their military?"

"They'll pay us. The problem is nobody ever asks," he added.

Prince Mohammed downplayed any apparent rift with the US leader and said relations between the two allies remain strong.

"You have to accept that any friend will say good things and bad things. So you cannot have 100 per cent friends saying good things about you," he said.

"You will have some misunderstandings. So we put that in that category".