Ljubljana - Prime Minister Janez Janša has labelled the atrocities Russia is believed to have committed in Bucha, a city close to Kyiv, crimes against humanity, likening them to the execution of Poles in Katyn in 1940 by the Soviet Union.

"These are massive crimes against humanity," he said on Twitter yesterday, noting that the Russian army behaved "as a horde of KGB executioners at Katyn."

"After seeing #BuchaMassacre, we are terrified to even imagine what we will see in #Mariupol," he said.

In a subsequent series of tweets, he suggested the West could have prevented that by giving Ukraine and Georgia a path to NATO membership in 2008.

"Summit 2008 was its beginning. The evil was encouraged there, the lessons of history forgotten. I had been there. I'm still ashamed remembering that Putin was invited, but the presidents of Ukraine and Georgia were not," he said.

According to Janša, this is why Germany and France, members of the "old Europe" that opposed membership action plans for Ukraine and Georgia, now have "a moral duty to help Ukraine".