Poland is likely to request consultations under NATO’s Article 4 after a reportedly Russian-made missile struck Polish territory near the Ukrainian border, and to raise the issue at a United Nations meeting. According to officials, the Security Council will meet on Wednesday.

Two people were killed in an explosion in a village 6 kilometers (3.5 miles) from the border, according to Polish President Andrzej Duda, who stated that Poland lacked conclusive evidence as to who fired the missile.

The incident happened hours after President Volodymyr Zelenskiy outlined to leaders of G20 nations his peace plan for Ukraine, and after Russia unleashed what Kyiv said was the heaviest wave of missile strikes in nearly nine months of war.

The United States and its NATO allies are investigating the incident in Poland, but early information suggests it may not have been caused by a missile fired from Russia, U.S. President Joe Biden said.

Russia’s defence ministry denied the reports that Russian missiles hit the Polish territory.

Duda said that he has informed NATO Secretary General Jens Stoltenberg and Biden that it is “highly probable” that the Polish ambassador to NATO “will request to invoke Article 4, that is consultations among the allies.”

Stoltenberg will hold urgent talks on Wednesday with alliance ambassadors over the incident, a spokeswoman and diplomats said on Tuesday.

According to Article 4 of the military alliance’s founding treaty, members can bring any issue of concern, especially related to security, for discussion, allowing for more time to determine what steps to take.

If it is determined that Moscow was to blame for the blast, it could trigger NATO’s principle of collective defense known as Article 5, in which an attack on one of the Western alliance’s members is deemed an attack on all, starting deliberations on a potential military response.

“All the leaders with whom I spoke with today assured me of allied support, inclusive of upholding all the provisions of (NATO’s) Art. 5,” Duda said on Twitter. “We will consider this matter together.”

Poland will also raise the matter at the United Nations Security Council meeting on Wednesday, Krzysztof Szczerski, Poland’s ambassador to the United Nations, said.

“On Wednesday, at the afternoon session of the U.N. Security Council, I will present the Polish position on the current situation,” Szczerski said on Twitter.