The UK Government is looking into reports that Russian missiles crossed into Poland on Tuesday.
It comes after a senior US intelligence official said Russian missiles had landed in the Nato member state close to the border with Ukraine, reportedly killing two people.
It is understood that the Government is aware of the reports, which emerged on Tuesday evening, and is urgently seeking clarity.
News of the explosion immediately prompted alarm amid fears of any escalation in Ukraine’s conflict with Russia, with several European leaders issuing urgent responses to the reports.
However, little information is so far known about how the incident might have occurred.
Nato secretary general Jens Stoltenberg said he had spoken to Polish President Andrzej Duda and that Nato was “monitoring the situation”.
“Allies are closely consulting. Important that all facts are established,” he tweeted.
A spokesperson for the US National Security Council also said it was looking into the reports.
A number of European leaders expressed concern about the reports, with European Commission president Ursula von der Leyen among those registering her alarm.
She tweeted: “Alarmed by reports of an explosion in Poland, following a massive Russian missile strike on Ukrainian cities.
“I extend my condolences and my strongest message of support and solidarity with Poland and our Ukrainian friends.”
A Polish government spokesman earlier said top leaders were holding an emergency meeting due to a “crisis situation”.
The official Twitter account of the Polish presidency said that Mr Duda had spoken to US President Joe Biden and Ukrainian President Volodymyr Zelensky following the explosion.
Polish media reported that two people died on Tuesday afternoon after a projectile struck an area where grain was drying in Przewodow, a Polish village near the border with Ukraine.
