Polish president says apparent missile strike in Poland was ‘isolated incident,’ but notes the ‘North Atlantic Alliance is on standby’

© Provided by CNBC Polish security forces investigate in Przewodow village near the Ukrainian border, where two Poles were killed by a suspected missile strike.

The president of Poland said his government doesn’t yet conclusively know who fired a missile that struck Polish territory late Tuesday, killing two civilians.

The explosion, which took place about 15 miles (24 km) from the Ukrainian border, came as Russia was launching a massive wave of missiles at Ukrainian cities and energy facilities just before dusk local time.

President Andrzej Duda said the projectile was “Russian-made” and variously referred to it as either a missile or a rocket.

“What happened was an isolated incident,” said Duda, who added that an investigation is underway. “There is no indication that more will take place”

Poland is a member of NATO. The development set off a chain of diplomatic activity among members of the alliance and Ukraine, which is not a NATO member but which gets massive military aid from the alliance.

U.S. President Joe Biden spoke with Duda and “offered full U.S. support for an assistance with Poland’s investigation,” the White House said. “President Biden reaffirmed the United States’ ironclad commitment to NATO.”

Warsaw was also in communication with NATO Secretary General Jens Stoltenberg, U.K. Prime Minister Rishi Sunak, French President Emmanuel Macron and German Chancellor Olaf Scholz.

“The North Atlantic Alliance is on standby,” Duda said. “We have strengthened the readiness of the Polish armed forces, including the air defense. Our planes will be supported by allied planes. We act calmly and prudently.”

Moscow offered no comment. Ukrainian President Volodomyr Zelenskyy assured Warsaw that “it was a rocket launched from the territory of the Russian Federation,” Duda said.

Poland’s Minister of Foreign Affairs Zbigniew Rau summoned the ambassador of the Russian Federation “and demanded immediate detailed explanations,” Poland’s Foreign Ministry said.

Biden, Macron, China’s Xi Jinping and other global leaders are gathered in Bali, Indonesia, for the Group of 20 summit.

— NBC News’ Ewa Galica contributed to this report.

This story is developing. Please return for more updates.