Polish Prime Minister Donald Tusk said on Wednesday that Russia was planning an "act of aerial terrorism" by planning a wave of firebomb attacks that could bring down aircraft in flight around the world.

Tusk added that Warsaw has been involved in countering "acts of sabotage" carried out by Russia, before referencing the burning package attacks in Britain, Germany and Poland this summer.

"The latest information confirms fears that Russia is planning not only aerial terrorism against Poland," Tusk told a news conference in Warsaw, without providing further details or explanation.

In July, DHL packages were exposed at a warehouse in Birmingham and on the tarmac at Leipzig Airport. Media reports said the Leipzig package was about to be loaded onto the plane, while the Birmingham package traveled on the plane and started a fire.

Two other incendiary devices have been discovered in Poland, and Western leaders and intelligence officials believe a crude plot to mail incendiary bombs through packages was orchestrated by Russia as a rehearsal for further attacks in the United States.

A New York Times report earlier this week said senior White House officials reviewed details of potentially eavesdropped conversations between senior officials in Russia's GRU military intelligence service. Russia described the incendiary devices as a test run for an attack on the United States, the newspaper reported.

U.S. President Joe Biden sent senior officials to warn Russian leader Vladimir Putin through his counterparts that Washington would hold Moscow accountable for "facilitating terrorism" if the plot develops further.

The devices exposed in Birmingham and Leipzig were originally shipped from Lithuania, with at least one concealed inside a massager. This simple method appears to expose a weakness in the package service's security scans.

Security procedures are said to have been quietly tightened, but few statements have been made to reassure the public.

In September, Thomas Haldenwang, then head of Germany's domestic intelligence agency, told the Bundestag that if the Leipzig package started burning during the flight, "it would lead to a crash."

Photos of the Birmingham fire published by The Guardian in December showed bright flames bursting out of a box of parcels being carried by an electric vehicle, suggesting the havoc could be caused if the parcels were ignited in mid-air.

The light emitted is consistent with that of a magnesium-based combustion device. Magnesium fires are difficult to extinguish and can become more severe if water is used, which may not be readily available to low-pressure crews. Use a special dry powder fire extinguisher instead.

The Russian Foreign Ministry did not respond to a request for comment. Moscow has frequently denied involvement in delivery warehouse bombings as well as break-ins, arson and attacks on individuals that Western officials say were carried out by agents hired by Russia.