European aviation authorities remain at a loss as to who or what is behind fake bomb threats that have caused dozens of flights to make emergency landings all across Europe, some with military escort. The lack of evidence hasn’t prevented Russia from being blamed, however.

“It remains unclear who is behind the airline threats, which come at a time of increased geopolitical tensions and warnings from authorities that Russia may be ramping up its so-called hybrid threats in Europe—a mix of covert and indirect attacks attributed to Moscow and meant to destabilize European countries,” AP reported on Saturday. “Authorities haven’t attributed the threats to any group or state actor, and no evidence has emerged linking the hoaxes to a government.”

Theories abound nonetheless. The focus on Europe means “there could be a Russian angle,” said Matthew Borie of Osprey Flight Solutions, which advises airlines on flight threats. “We need to keep in mind, though, that Iranian hybrid warfare is just as active in certain pockets of Europe as well.”

Adding to hysteria stemming from the bomb threats have been cyberattacks on supermarket refrigeration systems and security threats aimed at three European broadcasters—the Irish national broadcaster, RTE; the U.K.-based Sky and NOVA TV; a private broadcaster in Bulgaria—"a possible sign the menace was spreading beyond the skies,” AP claims.