United States President Donald Trump's backing of Russia over his own intelligence agencies is a matter for the US Congress and the American people to sort out, Foreign Affairs Minister Winston Peters says.

Peters, who is Acting Prime Minister, told Radio NZ today Trump's actions in recent days were "bewildering".

"I've always been ultra-cautious when it comes to intelligence agencies. We all recall the second Iraq conflict, based on the weapons of mass destruction and the information that the West was fed, by both sadly the US and the UK, only to be proven wrong," Peters said.

"That said, I really think that these are extraordinary days. But in the end they are for the US Congress and the US people to sort out, and they are the only people who can sort them out."

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Peters said evidence was yet to be laid out that would prove the scale of Russian meddling in the 2016 US election.

"I'm waiting for the process to prove the level of guilt."

Of Trump's actions in recent days, Peters said: "I'm bemused, we're all confused, we're all bewildered. But at the end of the day, this is a decision that the American people, in terms of the continuance of that sort of representation, have to make and only they can make."

Trump has cast doubt on the conclusion of US intelligence agencies that Russia interfered in the 2016 presidential election, saying after his summit in Helsinki with Russian President Vladimir Putin that Putin gave him a "very powerful" denial.

After Putin said his Government played no role in trying to sabotage the US election, Trump offered no push-back and went on to condemn the Justice Department's investigation of Russian interference as "a disaster for our country".

Peters said if the allegations were proven, "piece by piece, wherever they may be, then the world is a far worse place for it".

But he said the allegations were being led by the media.

"Actually the meddling in the US election is a full-on assertion that's being made now by the media, Washington-led in the main."

A dozen Russian intelligence officers have been indicted in the United States on charges of election interference.