Poland said early Wednesday that a Russian-made missile fell in the eastern part of the country

killing two people in a blast that Ukrainian President Volodymr Zelenskyy decried as “a very significant escalation” of the war.

Zelenskyy’s comments, delivered in an evening address to the nation, came hours after a senior U.S. intelligence official told The Associated Press that Russian missiles had crossed into Polish territory and killed two people.

A second person said that apparent Russian missiles struck a site in Poland about 15 miles from the Ukrainian border.

Elsewhere, President Joe Biden convened an emergency meeting of the Group of Seven and NATO leaders in Indonesia for consultations on the situation in Poland.

On Twitter, Biden promised “full U.S support for and assistance with Poland’s investigation,” and “reaffirmed the United States’ ironclad commitment to NATO.

The U.N. Security Council also planned to meet Wednesday for a previously scheduled briefing on the situation in Ukraine. The strike in Poland was certain to be raised

Poland’s statement did not address whether the strike could have been a targeting error or if the missile could have been knocked off course by Ukrainian defenses.

In their statements, Poland and NATO used language that suggested they were not treating the missile blast as an intentional Russian attack, at least for now. A NATO statement called it a “tragic incident.”