US President Donald Trump on Thursday said Russian President Vladimir Putin would not attack a Nato member, while downplaying reports that CIA Director John Ratcliffe had warned Russian officials against any such move during his recent visit to Moscow.

"He's not going to attack a Nato territory," Trump told reporters in the Oval Office.

Trump had earlier told Axios in a phone interview that he did not expect any Russian attack on Nato and said Ratcliffe had not been sent to Moscow to deliver a specific warning.

"Ratcliffe sees his Russian counterpart once every six months or once every year. They have a very good relationship. There was no message and there was nothing unusual," Trump told the news outlet.

European and U.S. intelligence officials have long monitored Russian sabotage and grey zone attacks in Europe that fall below the threshold of full-on war and are generally aimed at weakening Nato's unity and its member states' willingness to support Ukraine against Russian aggression.

The Kremlin on Thursday dismissed as "scare stories" US media reports suggesting that Russia could attack Nato, following a rare visit by the CIA director to Moscow.

US President Donald Trump and a senior EU official also played down the risk of Russian aggression.

The Wall Street Journal and CBS News reported that CIA Director John Ratcliffe had sought to dissuade Russia from attacking Nato members, amid US intelligence assessments that Moscow could seek to test the alliance.

The Journal reported that President Vladimir Putin could test Nato with a "limited assault" within the next few years.

Asked to comment on the reports at a daily briefing, Kremlin spokesman Dmitry Peskov said: "A lot of such scare stories are being published right now. Of course, they have nothing to do with reality."

On Ukraine, he said Russia "would prefer to achieve its objectives by peaceful means, but in the absence of an opportunity to do so, it is continuing the special military operation", referring to Moscow's ongoing Ukraine offensive.