TAMPA, Fla. (WFLA) — U.S. intelligence officials said two Polish residents were killed after a Russian missile strike in Ukraine went over the two countries’ borders. While the Polish government has not officially confirmed the deaths, its leaders are “meeting due to a ‘crisis situation'” according to reporting by the Associated Press.

According to the AP, Ukrainian President Volodymr Zelenskyy said Russia fired upwards of 85 missiles, aimed at Ukrainian infrastructure. Some of those missiles went over the border with Poland and into a village, killing two people.

NBC News reported that President Joe Biden’s national security adviser, Jake Sullivan, said in a statement that the United States “strongly condemns Russia’s latest missile attacks against Ukraine,” adding that they “will serve to only deepen the concerns among the G‑20 about the destabilizing impact of Putin’s war.”

Unlike Ukraine, Poland is a member of the North Atlantic Treaty Organization, or NATO. With missiles landing beyond Ukraine’s borders, there’s a possibility that NATO involvement in the conflict expands.

The NATO agreements made by the United States and other member nations includes a mutual defense pact, known as Article V of the Washington Treaty, “collective defense.”

According to the pact, NATO collective defense means “an attack against one Ally is considered as an attack against all Allies.”

The first time Article V was invoked was after the terrorists destroyed the World Trade Center on Sept. 11, 2001. Since then, NATO says the organization of countries has “taken collective defence measures on several occasions, including in response to the situation in Syria and the Russian invasion of Ukraine.”

However, NATO is not currently actively engaged in direct conflict with Russia as a result of its February 2022 invasion of Ukraine. Despite efforts to join NATO, Ukraine is not a member nation.

Should Poland invoke Article V, there’s a likelihood that U.S. troops could be called to the battlefield. Following Russia’s invasion, a regiment of troops from the Florida Army National Guard’s 53rd Infantry Brigade Combat team were stationed in Ukraine were ordered to leave and go to other parts of Europe.

“The Secretary made this decision out of an abundance of caution — with the safety and security of our personnel foremost in mind — and informed by the State Department’s guidance on U.S. personnel in Ukraine,” Pentagon Press Secretary John F. Kirby said in February. “This repositioning does not signify a change in our determination to support Ukraine’s Armed Forces, but will provide flexibility in assuring allies and deterring aggression.”

According to NATO, “Collective defense measures are not solely event-driven. NATO has a number of standing forces on active duty that contribute to the Alliance’s collective defense efforts on a permanent basis. These include NATO’s standing maritime forces, which are ready to act when called upon. They perform different tasks ranging from exercises to operational missions, in peacetime and in periods of crisis and conflict.”

The missile strikes by Russia follow the country’s military leaving contested Ukrainian city, Kherson. The Associated Press reported Ukraine had calmed slightly following weeks of drone and missile attacks. Zelenskyy warned that more Russian s trikes could come and urged his people to seek shelter.

For now, next steps for NATO member nations, and Ukraine, are uncertain.