The packages that exploded at transport hubs in Europe were a test piece of a Russian plot to cause explosions on cargo planes on flights to the United States, security officials say, writes the British agency Reuters.
Western governments and intelligence agencies in Europe have previously pointed to Moscow as the source of a series of fires and sabotage in Europe aimed at destabilizing Ukraine's allies.
However, explosions at courier service depots in Great Britain, Germany and Poland in July, which an adviser to the Lithuanian president said were the work of Russia, had the potential to bring about a severe escalation by causing explosions on planes as well.
"I can say that this is part of unconventional operations against NATO countries undertaken by Russian military intelligence services," Kestutis Budris, national security adviser to Lithuanian President Gitanas Nauseda, told Reuters on Tuesday.
"These operations are escalating: their focus is shifting ... to damaging infrastructure and to actions that could lead to the death of people," he added.
The Russian government did not immediately respond to a Reuters request for comment.
The Wall Street Journal quoted Western security officials on Monday as saying the devices that caught fire at U.S. DHL depots in Birmingham, central England, and Leipzig were part of a Russian operation aimed at starting cargo fires. or passenger planes on flights to North America.
The U.S. Transportation Security Administration said that over the past few months, it "worked with partners to introduce additional security measures for U.S. aircraft operators and foreign air carriers in connection with certain cargo shipments to the United States," writes Reuters.
Poland said in October it had arrested four people in an investigation into explosive packages sent by courier services to EU countries and Great Britain as part of a plot to target packages that would eventually reach the United States and Canada.
The Canadian government said on Tuesday that it had told Russia directly "that any threat to the safety and security of Canadians is unacceptable," although "there is no immediate threat at this time."
She added that she "takes threats to aviation security very seriously and cooperates closely with key national and international actors".
Warsaw blamed foreign intelligence services, without naming Russia specifically.
The Polish daily "Gazeta Viborcha" reported in October that a package caused a fire in a courier company's truck near Warsaw and that the packages that exploded in Poland, Germany and Britain were sent from Lithuania.
Lithuanian Prosecutor General Nida Grunskiene told reporters that Vilnius was investigating the packages and that arrests had been made "in Lithuania and elsewhere", but in the interests of the investigation she did not say how many people.
"Our investigation is going on quite intensively, in cooperation with institutions in other countries," she said.
The FBI declined to comment, as did the British Home Secretary.
Britain's MI5 director general Ken McCallum said in October that Russia's military intelligence agency GRU was trying to cause "chaos" across Britain and Europe.
In October, Poland announced that it would close the Russian consulate in the city of Poznań due to suspicions that it was the center of sabotage attempts, Reuters concludes.
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