Representatives of the NATO military alliance will meet Wednesday on the basis of NATO’s Article 4 following an explosion in Poland near the border with Ukraine that killed two Polish citizens.

Poland’s foreign ministry claimed the explosion was caused by a “Russian-made missile,” noting that Poland had “summoned the ambassador of the Russian Federation.”

Polish officials said the attack took place amid “another massive shelling of the entire territory of Ukraine and its critical infrastructure, conducted by the armed forces of the Russian Federation.”

In response to the explosion, Poland moved to invoke Article 4 of the NATO treaty, which allows NATO members to carry out consultative discussions about whether to invoke NATO Article 5, the alliance’s collective defense agreement, Reuters reported.

Poland reportedly scrambled fighter aircraft and placed its military and police forces on heightened alert. The country’s foreign ministry also said that it would expand the number of troops stationed at its border with Ukraine.

Russia’s foreign ministry denied Poland’s allegations, declaring, “No strikes on targets near the Ukrainian-Polish state border were made by Russian means of destruction,” adding that the explosion “has nothing to do with Russian weapons.”

Speaking at the G20 summit in Indonesia, US President Joe Biden said it was “unlikely” that the missiles that hit Poland were fired from Russia. Asked whether Russia had fired the missile, he replied: “There is preliminary information that contests that. It is unlikely in the lines of the trajectory that it was fired from Russia, but we’ll see.”

Biden also held an emergency meeting of the G7 countries (United States, Germany, Britain, France, Italy, Japan and Canada) over the bombing. NATO sources told Reuters that Biden stated at this meeting that the missiles that fell on Polish soil were anti-aircraft missiles fired by Ukraine.

Earlier, however, Ukrainian President Volodymyr Zelensky had categorically blamed Russia for the attack, calling the move a “very significant Russian escalation” and an “attack on collective security.”

Zelensky added, “Today, Russian missiles hit Poland, the territory of our friendly country. People died… It’s only a matter of time before Russian terror goes further… We must act.”

In a tweet, Ukrainian Foreign Minister Dmytro Kuleba called for the United States to respond by sending advanced fighter aircraft to Ukraine and establishing a no-fly zone.

Kuleba called on NATO countries to arm “Ukraine with modern aircraft such as F-15 and F-16, as well as air defense systems, so that we can intercept any Russian missiles. Today, protecting Ukraine’s skies means protecting NATO.”

The missile strikes came the same day as Russia launched one of its largest attacks on Ukrainian power infrastructure since the start of the war, and the first large-scale missile attack since Russia’s withdrawal from the city of Kherson.

The same day as the still unexplained explosion in Poland, the White House called on Congress to pass yet another massive military spending package for the proxy war with Russia in Ukraine.

The White House requested $47.7 billion in funding for the war, including $21 billion for weapons. This figure would more than double the total amount spent on US weapons shipments to Ukraine, which have up to this point amounted to $18.2 billion.

In addition to the weapons purchases, the bill would approve another $14 billion in direct budget subsidies to Ukraine.

Speaking at the G20 summit in Bali, Indonesia, Biden said that after the US election the US would further escalate its foreign policy goals of “competition” with Russia and China.

“The election held in the United States,” Biden said, “has sent a very strong message around the world that the United States is ready to play.”

“In the area of foreign policy, I hope we’ll continue this bipartisan approach of confronting Russia’s aggression in Ukraine,” Biden said earlier this week.

Even as the United Sates continues to flood Ukraine with weapons, press reports have made clear the extent of direct US involvement in the war.

Contradicting previous Ukrainian denials, the New York Times published an article Tuesday confirming that Ukraine was responsible for last month’s attack on Russian warships in the Black Sea.

The article reported, “Ukraine and its allies have been testing remote-controlled boats packed with explosives in the Black Sea, culminating in a bold attack in October against Russia’s fleet off the coast of Sevastopol.”

The article noted that US military planners are treating the Ukraine war as a “Beta Test” for trying out advanced US military hardware.

In July, Ukrainian Defense Minister Oleksii Reznikov openly declared that the country should be viewed as a “testing ground” for US defense contractors. “We are inviting arms manufacturers to test new products here,” he said.

Earlier this month, the Pentagon confirmed that active-duty US military personnel were operating inside Ukraine, including Marines guarding the US embassy and Pentagon officials directing the distribution of US arms shipments to Ukraine.

In October, veteran journalist James Risen reported that the Biden administration had authorized the clandestine deployment of US Special Forces in Ukraine. “Clandestine American operations inside Ukraine are now far more extensive than they were early in the war,” wrote Risen.

In July, the New York Times reported that dozens of US ex-military personnel are operating on the ground in Ukraine and that retired senior US officers are directing portions of the Ukrainian war effort from within the country.