NATO Article 4 has now been triggered nine times in the past 75 years, two of which have occurred in less than two weeks.

The organisation has called a meeting in Estonia early next week to discuss Russia’s incursion into Estonia’s airspace on Friday. The meeting comes after Estonia requested consultations under Article 4 of the Washington Treaty.

Article 4 states that members of NATO can bring an issue forward for the North Atlantic Council, the organisation’s principal political decision-making body, to consult. The parties will consult together whenever, in the opinion of any of them, the territory, political independence or security of any of them is threatened.

Since NATO was established in 1949, Article 4 has been invoked nine times, including today’s request. On 10 September, it was triggered by Poland after Polish forces shot down 19 drones over its airspace.

Article 5 states that "the Parties agree that an armed attack against one or more of them in Europe or North America shall be considered an attack against them all."

If members decided that Russia had attacked the territory of a member state, then Article 5 would be invoked and members would take the action they deemed necessary.

Article 5 is the cornerstone of the North Atlantic Treaty, NATO’s founding treaty. When the treaty was created in 1949, its key aim was to counter the Soviet Union if it sought to extend its control of Eastern Europe.

Republican and Democratic senators are seeking a bill which would target Russia’s “shadow fleet”.

The "Sanctioning Harbors and Dodgers of Western Sanctions," or SHADOW Fleets Act, would provide a list of indicators the US could use to identify vessels supporting the fleet, making it easier to sanction them sooner.

It would also put in place strict sanctions liability for any ship that engages in a transfer with a sanctioned Russian vessel.

US Senator Jim Risch said: “Putin will use every trick in the book to evade U.S. sanctions, and the U.S. is cracking down on this illicit shadow fleet of ships that he uses to fund his war.

“These ships and the oil sales they facilitate directly threaten American and European security, and will be stopped.”

Volodymyr Zelensky has said that Ukraine and its partners have laid the groundwork for long-term security guarantees and that he hopes to gauge how close they are to finalizing such commitments during next week's meetings in New York.

He said European nations are prepared to move forward with a framework if the United States remains closely engaged. He noted that discussions have taken place at multiple levels, including among military leadership and general staffs from both Europe and the US.

"I would like to receive signals for myself on how close we are to understanding that the security guarantees from all partners will be the kind we need," Mr Zelensky said.

He said sanctions against Russia must remain on the table if peace efforts stall, and that he plans to press the issue in talks with Trump.

"If the war continues and there is no movement toward peace, we expect sanctions," he said, adding that Trump is looking for strong steps from Europe.

UK officials have joined leaders across Europe in condemning Russia’s incursion into Nato airspace on Friday night.

Defence Secretary John Healey said: “This is yet another edition of the Putin playbook.

“Putin’s aggression only serves to strengthen the unity of NATO and our resolve to stand with Ukraine.”

Foreign Secretary Yvette Cooper said the UK was standing in solidarity with its Estonian allies, calling the incursion “reckless”

“We must continue to increase pressure on Putin, including driving forward the important new economic sanctions announced by the UK & EU in recent days,” she said.

A large-scale Russian missile and drone attack struck multiple regions across Ukraine early on Saturday, killing at least three people and wounding dozens, Ukrainian officials confirmed.

President Volodymyr Zelenskyy stated the assaults impacted nine regions, including Dnipropetrovsk, Mykolaiv, Chernihiv, Zaporizhzhia, Poltava, Kyiv, Odesa, Sumy, and Kharkiv.

“The enemy’s target was our infrastructure, residential areas and civilian enterprises,” he said, adding that a missile equipped with cluster munitions struck a multi-story building in the city of Dnipro.

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Defence secretary John Healey said the use of British fighter planes sent “a clear signal: Nato airspace will be defended”.

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Volodymyr Zelensky has said Ukrainian forces are inflicting “heavy losses” on the Russian military in a counteroffensive in the eastern Donetsk region.

Ukrainian troops pressed on with a frontline counteroffensive around the two cities of Pokrovsk and Dobropillia in the east of the country on Friday.

Russia said its forces had captured two new villages in their slow advance through Ukraine's east and south, but its Defence Ministry made no reference to the Ukrainian counter.

In his nightly video address, Mr Zelensky said the counteroffensive had disrupted Russian plans in their longstanding objective of seizing the key tactical city of Pokrovsk, which is a critical part of Ukraine’s supply line to the frontline. .

"It was there that one of the most important directions of the Russian offensive was located, and they were unable to launch a full-fledged offensive there. Our military is destroying their forces," Mr Zelensky said.

Italian Air Force F-35 fighter jets, currently deployed as part of the Nato Baltic Air Policing Mission, responded to Russia’s violation of Estonian airspace, according to the statement.

The Russian MIG-31 fighters entered Estonian airspace in the area of Vaindloo Island, which is a small island located in the Gulf of Finland in the Baltic Sea, the Estonian military said in a separate statement.