Former US president Donald Trump's complaints about some NATO allies not spending two percent of their GDP on defence are "nothing new", the Kremlin said Wednesday.

The 2024 presidential candidate drew fierce criticism from US President Joe Biden after he suggested he would encourage Russia to attack allies who failed to meet the spending target.

"This was one of Trump's main messages that he used in his relations with members of the alliance," Kremlin spokesman Dmitry Peskov told reporters.

"In fact, he constantly repeated this 'two percent' on various occasions. So there is nothing new in his approach to this problem," Peskov added.

At a campaign rally in South Carolina on Saturday, Trump described what he said was a conversation with a fellow head of state at a NATO meeting.

"One of the presidents of a big country stood up and said, 'Well, sir, if we don't pay, and we're attacked by Russia, will you protect us?' I said, 'You didn't pay, you're delinquent? No, I would not protect you,'" Trump told his supporters.

His comments about the US-led military alliance -- even by his standards of long-term NATO-bashing -- drew alarm from allies and fierce condemnation from the White House.

US President Joe Biden condemned the comments as "dumb" and "shameful" on Tuesday, in one of his most blistering attacks yet on his likely Republican rival.