Italian F-35 fighters attached to NATO's air defence support mission in the Baltic states were scrambled to intercept the Russian jets and warn them off, Estonian and Italian officials said, with alliance chief Mark Rutte praising the "quick and decisive response".

Sweden and Finland also scrambled rapid reaction aircraft, a spokesman for the Supreme Headquarters Allied Powers Europe (SHAPE) told reporters.

The alleged incursion came at a moment of heightened tension on NATO's eastern border, after Warsaw last week complained that around 20 Russian drones overflew its territory -- though the Kremlin denied targeting Poland.

"Three Russian fighter MiG-31 entered Estonian airspace in the Vaindloo Island area without permission, and remained there for approximately 12 minutes," the Estonian defence forces said.

"The fighter jets did not have flight plans, and their transponders were switched off. At the time of the airspace violation, the fighter jets did not have two-way radio communication with Estonian air traffic control."

NATO spokesperson Allison Hart called the event "yet another example of reckless Russian behaviour and NATO's ability to respond".

There was no immediate reaction from Moscow.

Later Friday, Estonian Prime Minister Kristen Michal said the Baltic country had "decided to request NATO Article 4 consultations" over the "unacceptable" violation.

It is the second time in under two weeks that a NATO country has invoked Article 4, under which a member state can convene urgent talks when it feels its "territorial integrity, political independence or security" are at risk.

Warsaw invoked Article 4 after it shot down what it said were Russian drones on September 9, with Romania complaining of a similar incursion days later.

Ukrainian President Volodymyr Zelensky -- whose country is at war with Russia -- on Friday accused Russia of expanding its "destabilising activity" with the series of airspace violations in Poland, Romania and Estonia.

"As threats escalate, so too will our pressure," said European Commission chief Ursula von der Leyen, who earlier in the day had presented for EU member state approval a 19th package of sanctions targeting Moscow over the Ukraine war.

Italy assumed command of the NATO Baltic Air Policing mission -- Operation Baltic Eagle III -- on August 1, with the Italian air force's F-35 aircraft taking responsibility for surveillance of Baltic airspace.

Russia has often tested Western air defences as its invasion of Ukraine grinds on, but Estonia complained that the sorties have become more provocative in recent months.

"Russia has already violated Estonia's airspace four times this year, which in itself is unacceptable. But today's incursion... is unprecedentedly brazen," Foreign Minister Margus Tsahkna said.

- Readiness tested -

"Russia's increasingly extensive testing of boundaries and growing aggressiveness must be met with a swift increase in political and economic pressure," he said.

Tsahkna said Russia's charge d'affaires in Estonia had been summoned to the foreign ministry to receive a formal complaint.

Earlier this month, Estonia complained that a Russian MI-8 helicopter had violated its airspace, also near the island of Vaindloo.

According to the Estonian defence forces, the helicopter entered the country's airspace for about four minutes without making contact with air traffic control.

It also did not have a flight plan, its transponder was turned off and it did not communicate with Estonian air traffic control. Similar incidents occurred on May 13 and June 22.

Last week, Poland and its Italian and Dutch NATO allies scrambled jets to intercept what it was around 20 Russian drones prowling its airspace. Some of them were shot down.

The UK, Germany and France announced plans to reinforce joint air patrols with more jets based on NATO's eastern flank.