Russia has tonight denied reports that its missiles killed two people after exploding in Poland, describing the reports as "deliberate provocation to escalate the situation" - and it's triggered concerns that NATO may be dragged into the conflict.
But what is NATO and why is it important?
A rural village in Poland - which is a NATO member - was hit by two Russian missiles that struck a grain silo and killed two people.
In the past, Russia has spoken out aggressively about Poland's role in getting supplies from NATO countries to Ukraine.
Some military experts warned the strike, if purposeful, could be a "test" of the west by Russian forces.
The claims came after a senior US intelligence official confirmed the incident that took place this afternoon.
Here's everything you need to know about NATO.
What is NATO?
NATO is the acronym for The North Atlantic Treaty Organization, whose members agree to a mutual defence pact.
Its 30 member states, which includes the UK, are expected to contribute two per cent of their GDP to defence, although that sum is not mandatory.
The combined military spending of NATO members makes up more than 70 per cent of the global total.
Headquartered in Brussels, Belgium, the organisation is based on a treaty signed in 1949 and hold periodical summits around the world.
NATO was created by the United States, Canada, and several Western European nations to provide collective security against the Soviet Union.
Ukraine is not a NATO member. Ukraine is a NATO partner country, which means that it cooperates closely with NATO, but it is not covered by the security guarantee in the Alliance’s founding treaty.
NATO’s actions are defensive, designed not to provoke conflict but to prevent conflict.
On its website, the alliance group said it had the "responsibility to ensure that this war does not escalate and spread beyond Ukraine, which would be even more devastating and dangerous".
What is Article 4?
Poland will reportedly ask NATO for Article 4 consultations over the projectiles that landed on its territory and killed two people.
The meeting will likely take place tomorrow morning, it's understood.
In Article 4 of NATO’s founding treaty, members can bring any issue of concern, especially related to the security of a member country, to the table for discussion within the North Atlantic Council.
Since the Alliance’s creation in 1949, Article 4 has been invoked several times, for instance by Turkey.
Consultation is a key part of NATO’s decision-making process because all decisions are made by consensus.
The consultation gives NATO an active role in preventive diplomacy by providing the means to help avoid military conflict.
What is Article 5 and why is it important?
NATO’s Article 5 focuses on the principle of collective defence - meaning each of its members is duty-bound to come to the aid of any other under attack.
This essentially means an attack on one NATO member is an attack on all NATO members.
For example, if a single British jet came under attack, all other 29 member states would regard it as an attack on one of their own.
Article 5 was used for the first time following 9/11, when the United States came under attack from terrorists.
There are issues that could arise if Article 5 is triggered though, because it has limitless potential for escalation.
Russia’s Foreign Minister, Sergei Lavrov said that a “Third World War will be nuclear, and devastating", in an undeniably sinister reminder of the stakes of escalation.
What happened in Poland today?
It's been reported that two Russian missiles exploded in eastern Poland, killing two.
The missiles landed at a grain silo and it is not yet known if it was a deliberate strike or an accidental impact.
A number of countries have already come out against Russia after the missile strike.
In Poland, the country's prime minister Mateusz Morawiecki convened the Committee of the Council of Ministers for National Security and Defence Affairs "as a matter of urgency", government spokesman Piotr Müller confirmed.
Müller said the meeting was being held due to a "crisis situation" and started at 8pm GMT this evening.
The missile struck a village north of the Ukrainian city of Lviv, which had regularly been targeted by Russian strikes.
Polish authorities and the army raced to the area and set up a cordon around the aftermath of the impact site.
Armed forces were reportedly on 'high alert' and military planes were said to be scrambled in response. They were in the air in the region.
Images emerging from the aftermath of the strike showed destroyed farm equipment and a large crater in the ground where the missiles exploded.
Prime Minister Rishi Sunak said the UK was “urgently looking into reports of a missile strike in Poland” and said the country would “support our allies as they establish what has happened”.
And Foreign Secretary James Cleverly said that the UK was “urgently looking into reports of missiles landing in Poland” and was in contact with NATO allies.
Meanwhile, the Pentagon took a firm line but refused to confirm the incident, and repeated previous promises of President Joe Biden : "When it comes to our security commitments and Article 5, we have been crystal clear: we will defend every inch of NATO territory."
