The Defence Secretary says the UK and its allies are "trying to all establish the facts" after a missile killed two people in Poland, close to the border with Ukraine.
Polish president Andrzej Duda said it is likely Ukraine launched the projectile whilst fending off a huge Russian air assault on Tuesday but said there is "absolutely no indication" it was an intentional attack.
Ben Wallace told Forces News "we will get to the facts in that case, but let's not forget missiles shouldn’t be flying around", adding: "We all know why this is happening.
"This is happening because Russia is illegally invading Ukraine.
"There's a marked difference here, we're all trying to work to establish the facts before we make some big statements.
"You never see that with Russia, they've usually decided the facts before the event happens and then announce that to the world and therein lies again the difference.
"There could be lots of capital for jumping on a bandwagon, but we're going to establish the facts, we act like professionals.
"But let's not forget in all of this, Russia is the aggressor."
The Kremlin denounced Poland's and other countries' initial reaction to the missile incident, saying it was not fired by Russian forces.
Ukrainian air defences worked furiously on Tuesday against the Russian assault on power generation and transmission facilities, including in Ukraine's western region that borders Poland. Ukraine's military said 77 of the more than 90 missiles fired were brought down, along with 11 drones.
Mr Duda said: "Ukraine's defence was launching their missiles in various directions and it is highly probable that one of these missiles unfortunately fell on Polish territory.
"There is nothing, absolutely nothing, to suggest that it was an intentional attack on Poland."
Mr Wallace said Russia launched the large-scale attack on Tuesday "for what seemed to be no apparent reason other than trying to terrify and kill civilians" and said the UK will not "shy away" from President Vladimir Putin.
Mr Wallace also said he messaged his Polish counterpart on Tuesday night and spoke to Prime Minister Rishi Sunak where the initial feeling was of "international solidarity".
"The second step is how can we support Poland and those neighbouring countries who may feel even more anxious.
"And thirdly, a reaffirmation of our determination to continue to support Ukraine until Putin fails in his invasion - and I think that is important."