NATO forces intercepted three Russian MiG-31 fighters on Friday after they entered Estonian airspace over the Gulf of Finland, triggering complaints of a dangerous new provocation from the transatlantic alliance and the European Union, but a denial from Moscow.

The Security Council will convene an emergency session Monday "in response to Russia's brazen violation of Estonian airspace", said a statement from the Estonian foreign ministry.

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 condemned as an "act of aggression".

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. I would."

Trump's at-times friendly relations with Russian President Vladimir Putin have appeared to fray as the latter continues to press his invasion of Ukraine despite the US leader's push for peace.

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.

- 'We don't like it' -

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

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

Asked whether he had been briefed on the situation in Estonia, Trump answered in the affirmative and added: "We don't like it."

That was a change in tone from his reaction to the Polish airspace incursion earlier in the month, which he said "could have been a mistake".

Monday's meeting at the United Nations marks the first time in 34 years of Estonia's UN membership that the European Union and NATO member -- a staunch supporter of Ukraine -- has officially requested an emergency Security Council meeting.

Estonian Foreign Minister Margus Tsahkna said the violation is "part of a broader pattern of escalation by Russia, both regionally and globally".

"This behaviour requires an international response," Tsahkna said.

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