Poland says the missile was probably an accident of the Ukrainian air defense system.

Poland said a rocket killed two people in a Polish town probably an accident possibly fired from Ukrainian anti-aircraft systems, a conclusion that allayed hours of tension over the source of an explosion on NATO territory.

A full investigation into the source is still ongoing after what appears to be an S-300 missile exploded Tuesday near Przewodów, a town near the Ukrainian-Polish border. That day, Russia had unleashed a barrage in Ukraine, sending dozens of missiles into Ukrainian territory, much of which targeted the country’s infrastructure. When the missile was reported in Poland, the possibility was immediately raised that it could have come from Russia – accidentally or deliberately – and with it the possibility of an escalation of the war in Ukraine if NATO were forced to respond.

At this point, NATO allies are largely lining up behind Poland, saying this was likely an errant Ukrainian missile, with little indication that it came from Russia. (The S-300 is a Soviet-era missile, and both Russia and Ukraine use themalong with some other European countries.) The White House said in a statement issued by National Security Council spokesman Adrienne Watson that the U.S. “has not seen anything contrary to President [Andrzej] Duda’s preliminary assessment that this explosion was most likely the result of a Ukrainian air defense missile which unfortunately landed in Poland.”

Yet the United States, Poland and other allies were quick to point out that, even if Ukraine was the source, it was an accident made possible because Russia unleashed another attack on Ukraine. “Ukraine had – and has – every right to defend itself,” the White House said.

However, Ukraine is reluctant to accept this conclusion. “I have no doubt it was not our missile,” Ukrainian President Volodymyr Zelenskyy has since said so. Ukraine has indicated that it wants to be closely involved in the investigation. (Russia, meanwhile, quickly denied any involvement since then exclaimed the Polish ambassador.)

For now, however, what could have been a potentially volatile and unpredictable situation seems largely resolved, even if it reminds the ever-present risks of an intentional or accidental escalation as the war continues along NATO’s borders.

A close call that is alarming, but perhaps not too surprising

Though there have been other close calls in this war, this is the first on NATO soil. NATO’s official response was a careful balance of waiting for more information, but also close cooperation between leaders. The tempered reactions showed that there was a prevailing desire not to increase tensions. Many heads of NATO-allied countries had already gathered in Indonesia for the G-20 and met there. NATO ambassadors also met, as well as European Union ambassadors. Poland called one national security meetingwhile continuing to coordinate with partners.

“NATO, the Polish government and our allies performed quite well in this way: the cool heads prevailed,” Michal Baranowski, senior fellow and director of the German Marshall Fund’s Warsaw office, said during a phone call with reporters. “There could have been, and there certainly was, a great rush to conclude that this was a deliberate attack by Russia. This would be an act of war and NATO should respond.”

It does not appear to be an act of war, at least based on the initial investigation. Poland is, of course, a member of NATO, an alliance based on the idea of ​​collective defense. In the aftermath of the attack, some (mostly on Twitter) began speculating that Poland might “trigger” Article 5, which basically says that an attack on one is an attack on all. As many pointed it out, this is a political decision – it’s not like all of a sudden, boom, you’re going to war – and usually very, very intoxicating consultations and discussions take place between alliance members before they even get to that very serious point. Article 5 has been called only once in the alliance’s history, in response to the September 11, 2001 attacks on US soil.

Article 4 of the treaty is the formalized consultation mechanism, where countries meet and discuss when one or more members feel threatened, and outline a course of action. (A bunch of Eastern European NATO members invoked Article 4 after Russia invaded Ukraine.) Article 4 is a deliberative tool that is supposed to find a way out of armed conflict.

In the end, Poland has not invoked Article 4, as some thought Warsaw could, especially since as tragic as the situation and civilian deaths are, the attack appears unintentional, and probably not even a rocket fired by Russia.

And yet, regardless of its origin, the missile was a reminder of how the conflict in Ukraine is playing out at the cutting edge; even a miscalculation threatens to turn this war into a larger conflict, possibly between two nuclear-armed actors.

Russian President Vladimir Putin, too, has repeatedly portrayed this as a proxy war between Moscow and Washington and the rest of the NATO alliance, and has issued explicit threats against the West. His warnings about the use of nuclear weapons add weight to questions about how the West should respond and deal with Russia.

The United States and its NATO allies have always maintained that they will not directly intervene in the conflict or deploy troops. But Ukraine’s struggle and economic survival depend largely on Western support, and the longer the war continues, the greater the military and financial commitment. The West’s decision to deliver advanced artillery to Ukraine helped troops recapture territory claimed by Russia; the anti-aircraft systems that Ukraine relies on to defend its airspace are also western donations.

As NATO leaders said, Ukraine has an absolute right to defend itself against Russian aggression and brutality, but it would be much more difficult without the support of the West. And Tuesday’s incident probably won’t change the calculus much; Russia launched nearly 100 missiles at Ukraine, targeting its already fragile civilian and energy infrastructure, likely to intensify discussions about the West donating even more defense systems and other advanced military equipment.

“Russia is facing adversity after adversity on the battlefield, and Russia is targeting Ukrainian civilians and civilian infrastructure,” US Defense Secretary Lloyd Austin said in a statement during the opening address at a meeting of the Ukrainian Defense Contact Group, which helps in coordinating support for Ukraine among the partners. “Both cases only strengthen the resolve of this Contact Group. And they only strengthen Ukraine’s resolve.”

But as long as the war continues, the risk of escalation also increases. NATO’s prudent and considered response is a sign that the alliance and its members are very, very careful about avoiding a more direct confrontation with Russia. As NATO Secretary General Jens Stoltenberg put it: “NATO is prepared for situations like this.” First, to prevent them from happening, but if they can’t, then to “make sure they don’t get out of hand”.