A NATO official has hit back at Donald Trump’s recent claims that the US might not come to the defence of partners who haven’t paid their way - reminding the Republican nominee of when the alliance was last used.

Referring to the critical “Article 5” of the treaty which deems an attack on one member state an attack on all, a NATO official told news.com.au: “The only time Article 5 was invoked was after 9/11 in defence of the US, when NATO sent AWACS [Airborne Warning and Control System] to patrol American skies and deployed a third of the troops in Afghanistan for over a decade, where over one thousand soldiers from non-US Allies and partners gave their lives.”

The comments come after Trump repeated his assertions the US may not be relied upon as the bedrock of the alliance that has been the defining feature of global security for decades.

On Sunday he told Meet the Press the US would make other countries pay their way in order to avoid being seen as “the stupid country”.

“Now, a country gets invaded. They haven’t paid. Everyone said ‘Oh, but we have a treaty’.” “We have countries within NATO taking advantage of us. With me, I believe they are going to pay,” he said.

“This isn’t 50 years ago. It’s not 30 years ago. We’re a different country today,” he said while also advocating a review of spending in other areas as well as World Trade Organisation rules.

“We take care of Japan. We take care of Germany and South Korea and Saudi Arabia and we lose on everything.”

“We can no longer be the stupid country.”

The issue over how much the US and other nations contribute to military spending has been a contentious one in the years following the financial crisis as many countries look for ways to trim the fat from their national budgets.

Trump’s comments prompted a warning from President Obama who said “anybody who’s been paying attention knows there is a big difference between challenging our European allies to keep up their defence spending, particularly at a time when Russia’s been more aggressive, and saying to them, ‘You know what? We might not abide by the central tenet of the most important alliance in the history of the world.’”

NATO Secretary-general Jens Stoltenberg said he will not interfere in the US election campaign, but solidarity is a “key value” among NATO allies.

“This is good for European security and good for US security. We defend one another. We have seen this in Afghanistan, where tens of thousands of European, Canadian, and partner nation troops have stood shoulder-to-shoulder with US soldiers,” he said.

“The United States has always stood by its European Allies. Now the US is stepping up its support once again, and increasing its presence.”

He said European Allies and Canada have improved their spending on defence in recent years and the organisation expects a further increase of three per cent or $10 billion.

“Two world wars have shown that peace in Europe is also important for the security of the United States,” he said.

Donald Trump will take part in a Reddit AMA on Wednesday evening US time.