Russia suspected of plot to send incendiary devices on planes: Sources

Russia schemed to send incendiary devices, shipped through a commercial carrier on planes that would potentially end up in the United States, according to sources familiar with the situation.

In Poland, four people were charged in connection with camouflaged explosives that "detonated during land and air transport" in the U.K. in July, according to a statement from the country's prosecutor's office.

"The group's activities consisted of sabotage and diversion related to sending parcels containing camouflaged explosives and dangerous materials via courier companies to European Union countries and Great Britain, which spontaneously ignited or detonated during land and air transport," the Polish prosecutor's office said in a statement.

"The group's goal was also to test the transfer channel for such parcels, which were ultimately to be sent to the United States of America and Canada," according to the statement.

"I'm not sure the political leaders of Russia are aware of the consequences if one of these packages exploded, causing a mass casualty event," Pawel Szota, the head of the foreign intelligence agency told The Wall Street Journal, which first reported the story.

ABC News has reached out to Szota for a comment.

The Kremlin on Tuesday dismissed reports about the alleged plot, with spokesperson Dmitry Peskov describing the allegations as "incoherent" and saying they weren't backed by "truthful information," according to Russian news agency Interfax.

The U.K.'s Metropolitan Police also confirmed that officers from the counter-terrorism unit are investigating the incident that occurred in Birmingham, England.

"On Monday, 22 July, a package at the location caught alight. It was dealt with by staff and the local fire brigade at the time and there were no reports of any injuries or significant damage caused," the Met said in a statement.

There have been no arrests made in the incident.

A U.S. official told ABC News that the Transportation Security Administration remains vigilant against threats to aviation and air cargo systems and said there is no current active threat targeting U.S.-bound flights.

The incident that occurred in England and another incident in Germany are believed to be part of a wider plot, according to a source familiar with the investigation.

A senior U.S. counterterrorism official confirmed to ABC News that the U.S. was alerted to the Russian effort over the summer. European officials told their American counterparts that they believed the Russians were trying to ship incendiary devices that would go off inside locations supporting the Ukrainian war effort to hinder Ukraine as it continues fighting the Russian invasion.

European officials said they do not believe the Russians were planning or trying to take down a commercial or cargo plane, the official said. But devices don't always work properly and the risks to commercial and civilian aviation are serious when incendiary devices are enabled and shipped.

TSA did not address the incidents abroad, but said in a statement to ABC News that the agency "continually adjusts their posture" and promptly shares any and all relevant information."

"Over the past several months, as part of a multi-layered security approach, TSA worked with industry partners to put additional security measures for U.S. aircraft operators and foreign air carriers regarding certain cargo shipments bound for the United States, in line with the 2021 TSA Air Cargo Security Roadmap," the statement said. "We greatly appreciate the cooperation and collaboration with industry as together we work to ensure the safety and security of air cargo."

ABC News' Joe Simonetti contributed to this report.