Russia-Ukraine updates: Putin suspends key US-Russia nuclear treaty in speech denouncing West

The missile that killed two people in Poland on Tuesday was apparently an "unfortunate accident," according to Polish President Andrzej Duda.

Duda said Wednesday that the projectile was "probably a Russian-made S-300 missile," according to The Associated Press.

"At the moment, we have no evidence that it was a missile launched by the Russian side," Duda added. "There are many signs that it was an air defense missile that, unfortunately, fell on the territory of Poland."

Following his meeting with leaders of the G-7 and NATO on Ukraine, President Joe Biden said Tuesday night that it's "unlikely" the missile that hit Poland was fired from Russia, but that the group would support the investigation into what happened.

When asked if it's too early to say whether the missile was fired by Russia, Biden responded: "There is preliminary information that contests that. I don't want to say that till we completely investigate, but it's unlikely in the minds of the trajectory that it was fired from Russia, but we will see."

"I'm going to make sure we find out exactly what happened," Biden said, and then determine the next steps, adding that there was "total unanimity" among leaders today on this decision.

The president added that recent Russian missile attacks were also a point of discussion this morning.

"They have been totally unconscionable, what they are doing, totally unconscionable," he said.

-ABC News' Justin Ryan Gomez

Polish President Andrzej Duda said Tuesday night that a rocket that landed near the Polish-Ukrainian border, killing two Polish citizens, may have been Russian-made. Though he said that there is no conclusive evidence at this time of who launched the missile and that an investigation is underway.

Duda said he has also spoken with NATO Secretary General Jens Stoltenberg and President Joe Biden.

Stoltenberg said earlier that NATO is monitoring the situation.

President Joe Biden spoke by phone with Polish President Andrzej Duda and "expressed deep condolences for the loss of life in Eastern Poland," according to the White House.

Biden "offered full U.S. support for and assistance with Poland's investigation" and the two agreed "they and their teams should remain in close touch to determine appropriate next steps as the investigation proceeds," the White House said.

Polish officials confirmed that two Polish citizens were killed in an explosion Tuesday in the area of Hrubieszów. They were the owner of a granary that was stuck and a tractor driver who was transferring corn to the facility, according to local officials.

-ABC News' Ben Gittleson and Tomek Rolski