Polish prosecutors said today that Russian intelligence services were likely behind a series of packages that exploded in July at courier centers across Europe, pointing to Moscow as the prime suspect in what could have been a plane crash.

Western diplomats have previously said that Russia is trying to destabilize Ukrainian allies through sabotage.

Explosions at courier centers in Britain, Germany and Poland in July had the potential to seriously escalate and cause an airplane explosion, according to authorities.

Security officials said the packages were part of a plan whose ultimate goal was to detonate cargo flights bound for the United States and Canada.

The evidence gathered in this case indicates a high probability that these sabotages were ordered by Russian special services, Polish prosecutor's spokesman Przemysław Nowak said in a statement.

The Russian Embassy in Warsaw did not immediately respond to a request for comment, having previously denied any involvement.

Novak added that the Polish authorities are looking for two Russians and that they detained four Ukrainians as part of the investigation. In October, Polish prosecutors said they had arrested four people and were looking for two more, but did not disclose the nationalities of the suspects. Prosecutors said in October they were investigating the role of "foreign intelligence services," without specifically naming Russia.

 We are conducting activities to identify the remaining persons involved in this international group, Novak said in a statement sent to the media today. According to him, the packages could have been sent from the capital of Lithuania, Vilnius