Poland suspects Russian intelligence services were behind an explosion on a major Polish railway line used to transport military goods and aid to Ukraine, an act Prime Minister Donald Tusk called an "unprecedented act of sabotage."

In the first comments where a Polish official suggested Moscow was behind the attack over the weekend, Jacek Dobrzynski, a spokesperson for Poland's special services minister, said the blast was an attempt "to destabilize" and "spread fear."

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In a speech to Polish lawmakers after the extraordinary meeting, Tusk said that Poland had identified two people responsible for sabotage on its railway.

He added the suspects are Ukrainian nationals who collaborated with Russian intelligence and fled to Belarus.

"The most important information is that...we have identified the people responsible for the acts of sabotage," Tusk said in an address to lawmakers in Warsaw.

"In both cases we are sure that the attempt to blow up the rails and the railway infrastructure violation were intentional and their aim was to cause a railway traffic catastrophe."

Map: Explosion And Alleged Sabotage On Warsaw-Lublin Railway

Tusk added Poland is raising the security alert level in some parts of the country and is developing plans for the military to protect key infrastructure, including railways.

The blast on November 17 occurred on a line running from Warsaw to the eastern Polish city of Lublin, about 100 kilometers (60 miles) from the border with Ukraine.

Poland's prosecutors have qualified the sabotage as terrorism saying it could have been carried out at the behest of a foreign power.

Polish Defense Minister Wadysaw Kosiniak-Kamysz announced security forces werereinforcing patrolsto watch over critical areas of the railway network in the east of the country, such as bridges, viaducts, tunnels, stations, and control systems.

Polish officials, as well as those from other European nations, have long accused Moscow is accused of waging a "hybrid" campaign of sabotage and spying against those countries that have aided Ukraine since Russia launched its full-scale invasion in February 2022.

Last month, Polish authorities arrested eight people suspected of spying or planning attacks on behalf of Russia.

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In January, Tusk accused Russia of plotting terror attacks against unspecified targets utilizing aircraft.

His comments came amid a growing number of suspicious, alarming, and unexplained incidents.

Some have involved international airlines and allegations Russia was seeking to plant secret explosives on cargo flights, while others involved ships that have disrupted undersea cables.

Moscow has routinely denied Western accusations of terror attacks, including arson, break-ins, poisoning, and attacks on individuals in the West.