NATO scrambled jets after three Russian MiG-31 fighters on Friday breached Estonian airspace for some 12 minutes, triggering complaints of a dangerous new provocation and a denial from Moscow.

Estonia, a NATO member, called for a meeting of the UN's top body, the Security Council, "in response to Russia's brazen violation of Estonian airspace", and talks with other NATO allies.

"As we said nine days ago, the United States stands by our NATO Allies in the face of these airspace violations. And I want to take this first opportunity to repeat, and to emphasize, the United States and our Allies will defend every inch of NATO territory," said US Ambassador Mike Waltz.

The incursion came after fellow NATO member Poland said earlier this month Russian drones had repeatedly violated its airspace during an attack on Ukraine, in what Warsaw called an "act of aggression."

US President Donald Trump on Sunday joined the condemnation of the latest airspace violation, vowing to defend Poland and the Baltic states in case of escalation from Russia.

Asked whether he would help defend the EU members if Russia intensifies hostilities, Trump told reporters: "Yeah, I would."

Trump's relationship with Russian President Vladimir Putin has blown hot and cold, with the Kremlin leader pressing his invasion of Ukraine and the US president urging peace but showing little concrete sign of pressuring Moscow.

Trump said Thursday at the close of a state visit to Britain that Putin had "really let me down" by continuing the war, now in its fourth year.

"At a time when President Trump and the United States has been focused, and spent an enormous amount of time and effort to end this horrific war between Russia and Ukraine, we expect Russia to seek ways to de-escalate -- not risk expansion," Waltz added in his maiden speech to the Council.

Western powers have warned that Russia is playing with fire with its repeated ventures into NATO airspace, whose members have a mutual defense assistance pact.

In the incident in Estonian airspace, Italian F-35 fighters attached to NATO's air defense support mission in the Baltic states, along with Swedish and Finnish aircraft, were scrambled to intercept the Russian jets and warn them off.