NATO made the intervention after Mr Trump said he would let Russia “do whatever the hell they want” to members of the alliance that don’t pay enough for defence at a rally in South Carolina on Saturday.
NATO has criticised comments made by Donald Trump at a campaign event – claiming they “put American and European soldiers at increased risk”.
The former US president had said he would let Russia “do whatever the hell they want” to members of the alliance that don’t pay enough for defence.
Joe Biden also denounced his Republican opponent’s comments as “appalling and dangerous”.
The 81-year-old president – who has himself been in the spotlight over a report that questioned his memory – said Trump was admitting to giving Putin “a green light for more war and violence” in Ukraine and to expanding “his aggression” to Poland and the Baltic States.
Mr Biden added: “Sadly, they are also predictable coming from a man who is promising to rule as a dictator like the ones he praises on day one if he returns to the Oval Office.”
He underlined that supporting US allies was “critical to keeping American people safe here at home”.
At a rally in South Carolina on Saturday, Mr Trump recalled an exchange with an unnamed “big country” who asked if they would be protected if Russia attacked them.
“I said: ‘You didn’t pay? You’re delinquent?’ No, I would not protect you. In fact, I would encourage them to do whatever the hell they want. You got to pay. You got to pay your bills,” he told the crowd.
In response, NATO said: “NATO remains ready and able to defend all allies. Any attack on NATO will be met with a united and forceful response.
“Any suggestion that allies will not defend each other undermines all of our security, including that of the US, and puts American and European soldiers at increased risk.
“I expect that regardless of who wins the presidential election the US will remain a strong and committed NATO ally.”
