Speaking after a meeting with Ukrainian president Volodymyr Zelenskyy on Wednesday, he told journalists: “Poland played a key role in Europe in counteracting acts of sabotage and diversion, which Russia organizes not only on Polish territory.

“Some acts of sabotage or preparations for diversion were very dramatic. I will not go into details about this latest information, but I can confirm the validity of these fears, that Russia was planning acts of air terror, and not only against Poland, but against airlines all over the world.”

Tusk did not say what acts he was referring to or elaborate on the contents of the information, but added: “Acts of sabotage, different versions of the war that Russia has declared against the entire civilized world, not just Ukraine, require joint action.”

The warnings follow reports on Tuesday that outgoing U.S. President Joe Biden allegedly warned Putin about Russian intelligence services preparing sabotage operations on board transatlantic flights.

According to the New York Times, a Kremlin-backed operation was to place self-igniting courier packages on board planes flying to the U.S. and Canada.

“The risk of a serious accident was real,” U.S. Homeland Security Secretary Alejandro Mayorkas was quoted as saying.

In response Biden ordered National Security Adviser Jake Sullivan and CIA Director William Burns to send a warning to Putin’s inner circle.

One official familiar with the operation told the New York Times that every possible step was taken to ensure the signal reached the Russian leader.

Sullivan spoke with Putin’s national security adviser, Yuri Ushakov, while Burns spoke with Sergei Naryshkin, head of the Foreign Intelligence Service (SVR), and Alexander Bortnikov, head of the Federal Security Service (FSB).

Security officials investigating a series of parcel explosions in July at courier depots in Britain, Germany and Poland warned that they could have exploded on an aircraft.

They added that the parcels were part of a plot that ultimately aimed to trigger explosions on cargo flights to the United States and Canada.

Polish Prosecutor’s Office spokesman Przemyslaw Nowak said in an emailed statement: “The evidence collected in the case indicates a high probability that the discussed acts of sabotage... were inspired by Russian security services.”