The incident occurred while Russia was firing scores of missiles at cities across Ukraine, in what Kyiv says was the most intense volley of such strikes of the nine-month war.

    Kyiv says it shot down most of the incoming Russian missiles with its own air defence systems. Ukraine's Volyn region, just across the border from Poland, was one of the many Ukraine says was targeted by Russia's countrywide attacks.

    The Russian Defence Ministry said none of its missiles had struck closer than 35 km (20 miles) from the Polish border, and that photos of the wreckage in Poland showed elements of a Ukrainian S-300 air defence missile.

    The Kremlin said on Wednesday some countries had made "baseless statements" about the incident, after having accused Poland of an "absolutely hysterical" reaction on Tuesday, but that Washington had been comparatively restrained.

    Hours after the incident, Ukrainian President Volodymyr Zelenskiy had blamed it on "Russian missile terror", and on Wednesday Kyiv did not appear ready to concede that its own missile was involved. Oleksiy Danilov, Secretary of Ukraine's National Security and Defence Council, said Kyiv wanted access to the site and still saw a Russian "trace" behind the attack.

    However, news that officials had concluded the missile was Ukrainian brought some relief to the inhabitants of the Polish village where the missile struck, who said they had feared being dragged into the war.

    "Everyone has in the back of the head that we are right near the border and that an armed conflict with Russia would expose us directly," Grzegorz Drewnik, the mayor of Dolhobyczow, the municipality to which Przewodow belongs, told Reuters.

    "If this is an a mistake of the Ukrainians, there should be no major consequences, but I'm not an expert here."

    Some Western leaders at a summit of the G20 big economies in Indonesia suggested that whoever fired the missile, Russia and President Vladimir Putin would ultimately be held responsible for an incident arising from its invasion.

    "They stressed that, whatever the outcome of that investigation, Putin's invasion of Ukraine is squarely to blame for the ongoing violence," British Prime Minister Rishi Sunak's office said after a meeting between Sunak and Canadian Prime Minister Justin Trudeau on the summit sidelines.

    G20 leaders issued a closing declaration saying "most members strongly condemned the war in Ukraine", although it acknowledged that "there were other views and different assessments of the situation and sanctions".

    Russia is a member of the G20 and Ukraine is not, but Zelenskiy addressed the summit by video link, while Putin stayed home.

Moscow launched Tuesday's wave of missile attacks just days after abandoning the southern city of Kherson, the only regional capital it had captured since the invasion.

    The barrage echoed a pattern of Moscow lashing out with longer-range missile volleys after losses on the battlefield to a continuing Ukrainian counter-offensive in the east and south.

    In Kherson, residents who crowded into the central square on Wednesday to obtain mobile phone cards and humanitarian aid took little notice of explosions from Russian artillery firing toward the city. Several impacts could be heard 3-4 km away.

    Tuesday's Russian missile flurry largely targeted Ukraine's energy grid, causing power blackouts in a number of cities, some far from frontlines. Millions of people were deprived of electricity, according to the U.N. humanitarian office OCHA.

    Rolling power outage schedules in the western Lviv region were being extended to cover all hours of the day, regional governor Maksym Kozytskyi wrote on Telegram on Wednesday.