Russian intelligence services are likely behind a series of parcels that exploded in courier depots across Europe, according to Polish prosecutors, in a case officials say could have caused an air disaster.

Western officials have previously said Russia has tried to destabilise allies of Ukraine with acts of sabotage.

The explosions in courier depots in Britain, Germany and Poland in July had the potential to develop into a serious escalation by causing an explosion on an aircraft.

Security officials have said the parcels were part of a plot that ultimately aimed to trigger explosions on cargo flights to the United States and Canada.

“The evidence collected in the case indicates a high probability that the discussed acts of sabotage … were inspired by Russian special services,” Polish Prosecutor’s Office spokesperson Przemyslaw Nowak said in a statement emailed to the Reuters news agency.

Moscow did not immediately comment on the Polish claims, but it has previously denied involvement.

Nowak said Polish authorities are searching for two Russians and have detained four Ukrainian citizens as part of their investigation.

Canadian diplomat summoned

Meanwhile, Russia summoned a Canadian diplomat on Friday to rebut Western allegations that Russia’s secret services were behind the plot.

Canadian media said this week that Ottawa had expressed its concern to Russian officials after Poland and Lithuania announced several arrests as a result of a probe into attempts to send parcels packaged with explosives on cargo flights to the US and Canada.

“The deputy head of the Canadian diplomatic mission in Moscow was summoned and handed an official note in connection with the false accusations of alleged planned ‘Russian sabotage’ against NATO countries,” Russia’s Ministry of Foreign Affairs said.

Moscow said the Canadian diplomat “was told that these speculations” were being spread in a “coordinated manner, in the context of the hybrid war” being waged against Russia by the West.

The alleged plot, involving civilian airlines, comes as concern grows in the West at what it sees as Russia’s increasingly reckless espionage and sabotage operations inside NATO countries.

“Russian intelligence services have gone a bit feral, frankly,” Richard Moore, head of Britain’s MI6 intelligence service, said in September in rare public remarks.