STORY: The United States and its NATO allies are investigating a blast that killed two people in Poland.
The explosion happened on Tuesday in the Polish village of Przewodow, about 3.5 miles from the border with Ukraine.
Photographs obtained by Reuters showed a damaged farm vehicle lying on its side next to a large crater.
Ukrainian and Polish authorities said the blasts were caused by Russian-made missiles.
Moscow has denied responsibility, but the incident raises fears the Ukraine war could spill over its borders.
Hours after the blast, U.S. President Joe Biden convened an emergency meeting of world leaders on the sidelines of the G20 summit in Bali.
Biden later said it was “unlikely” that the missile which struck the village was fired from Russia.
"...It is unlikely in the minds of the trajectory that it was fired from Russia. But we will see."
Following Biden's comments, it was reported in the Associated Press, citing U.S. officials, that initial findings suggested that the missile that hit Poland had been fired by Ukrainian forces at an incoming Russian missile.
Poland has been a member of NATO since 1999.
Under Article 5 of the defensive alliance, an attack on one country is considered to be an attack on all.
Two European diplomats said Poland had requested a NATO meeting within hours of the explosion under the treaty's Article 4.
It states that members can convene talks when under threat.
Poland's Prime Minister said the country was also increasing the readiness of some military units.
Russia's ambassador to Warsaw has also been summoned to provide an explanation.