Here’s what we know about the S-300 missile, which was involved in the Poland blast.

The rocket that caused a deadly explosion on Polish territory was an S-300 air defense missile, officials said on Wednesday — a munition that was built for air defenses but that also has been used by Russia to attack in Ukraine.

Both Russia and Ukraine possess the systems, which likely contributed to early confusion over who was responsible for the explosion that killed two people on Tuesday.

Polish and American officials on Wednesday downplayed the possibility that the rocket strike was intentional, citing early indications that it had been launched by Ukrainian forces to protect against incoming fire. President Andrzej Duda of Poland said the S-300 appeared to be a Soviet-era munition and “there is no evidence that it was launched by the Russian side.”

“It is highly probable that it was fired by Ukrainian antiaircraft defense,” Mr. Duda said.

The Polish justice minister, Zbigniew Ziobro, said that the remains of the S-300 were found at the site of Tuesday’s explosion in the village of Przewodów, near the border with Ukraine. He said Polish law enforcement officials and American experts were examining the impact zone.

In a post on Twitter, Mr. Ziobro also noted that the S-300 is “used by the Russian and Ukrainian armies” — signaling that determining its origins would take time.

Both Russia and Ukraine have depended on the S-300 systems, which are built by Russia, as protection against incoming air assaults during the ongoing war. But military officials and experts have said that Russia has increasingly turned to the S-300, a surface-to-air rocket, for hitting ground targets in Ukraine as its stockpiles of attack missiles dwindle.

The S-300 was first used in 1978 and can hit everything from aircraft to drones to ballistic missiles. Over the years, Russia has exported the systems across Asia and Eastern Europe, including to Syria, Iran and to Crimea after Moscow illegally annexed the Ukrainian peninsula in 2014.

Older generations of the rocket have a range of roughly 15 miles to 90 miles, according to the Center for Strategic and International Studies. Newer variants can hit targets up to about 120 miles away, according to Janes, a defense intelligence firm.