Russia has insisted it did not fire the missile that killed two people in a Polish village near Ukraine’s border.
A spokesman for the defence ministry told Russia’s state-owned RIA news agency that its strikes on 15 November were no closer than 22 miles (35km) from the Polish border.
They claimed that images of the site showed the wreckage to be that of a Ukrainian S-300 missile.
It comes as US President Joe Biden cast doubt on earlier claims by Ukrainian and Polish authorities that the missile which hit a grain silo in Przewodow was fired by Moscow.
Speaking after a meeting with G7 and NATO leaders, Mr Biden said: “There is preliminary information that contests that.
“I don’t want to say that until we completely investigate it, but it is unlikely in the lines of the trajectory that it was fired from Russia, but we’ll see.”
And three US officials have told the Associated Press news agency the missile could have been fired by Ukrainian forces at an incoming Russian missile.
They claim the Ukrainians had been trying to defend themselves against a Russian salvo aimed at their electrical infrastructure.
A spokesman for UK Prime Minister Rishi Sunak said: “I think, on all sides there’s agreement there needs further investigation before any conclusions are drawn.”
The missile had sparked worried talk of NATO’s Article 5, which means that an attack on a member country is seen as an attack on all allies.
US Pentagon spokesman Brigadier General Patrick Ryder said America would “defend every inch of NATO territory”.
But Polish President Andrzej Duda said his country is “very likely” to instead invoke Article 4 later today, which allows a member country to raise a security issue and have it discussed.
Mr Duda said: “We do not have any conclusive evidence at the moment as to who launched this missile… it was most likely a Russian-made missile, but this is all still under investigation at the moment.”
He added: “We are acting very calmly. What happened was a one-off incident.
“There are no indications that there will be a repeat.”
Meanwhile, Poland’s national security council (BBN) is set to meet later.
And Deputy Foreign Minister Pawel Jablonski said his country remained safe thanks to its NATO membership but warned that more incidents were possible.
“The reaction of our allies, their unequivocal support and willingness to stand by us, shows that we are a much safer
country than if we were not in NATO.
“As a country bordering Ukraine, we may be exposed to various types of incidents, including accidental ones.”
Lithuanian President Gitanas Nauseda said: “Lithuania will be actively support deploying (NATO) air defences along the Polish-Ukrainian border.
And he told reporters this also applied to the rest of the eastern flank, adding: “I hope by next year’s NATO summit in Vilnius we will be able to make progress, as the situation confirms it is the right decision and needs swift implementation.”
A spokesperson for the United Nations said that avoiding an escalation in the war is “absolutely essential”, adding that a “thorough investigation” should take place.
And a statement following a meeting of G7 leaders on Wednesday morning said: “We discussed the explosion that took place in the eastern part of Poland near the border with Ukraine. We offer our full support for and assistance with Poland’s ongoing investigation.”