The Polish services, in cooperation with international allies, have identified two suspects; their identities have not been made public as the operations are still ongoing, Tusk said in parliament.
The suspects are a man previously convicted of sabotage by a court in Lviv, western Ukraine, and another individual from the eastern Donbas region.
Tusk told lawmakers that the suspects had spent time in Belarus before carrying out the attacks in Poland, and that the Polish security services "now possess their full personal data and images."
The suspects have since left Poland via the Terespol border crossing, he said.
According to the Polish prime minister, they had been "working with Russian intelligence services for an extended period."
Tusk described the incidents, which he said aimed to cause "a major rail disaster," as "an unprecedented situation, the most serious of its kind since the beginning of Russia's invasion of Ukraine" in February 2022.
"In both cases, we are certain that these acts were deliberate," Tusk told parliament, adding that "a certain boundary has been crossed."
According to the prime minister, the first incident involved installing a metal clamp on the tracks, designed to derail a train.
A mobile phone with a power bank was found nearby, apparently set up to record the event. But the attempt was unsuccessful, Tusk said.
The second, more serious act of sabotage occurred on Saturday evening near the Mika station on the Warsaw-Lublin line, according to Tusk.
He detailed that a military-grade C4 explosive was detonated via a 300-metre-long electric cable as a freight train was passing.
The explosion caused only minor damage to a wagon floor, and the driver was reportedly unaware of the incident. Investigators secured unexploded material from the site.
In response to the threats, the Polish government has decided to raise the terror alert level, Tusk said.
He added that a "Charlie-CRP" alert level – the third-highest – would be introduced on selected railway lines following a request from the head of the Internal Security Agency and the interior minister.
An emergency meeting of the Government Committee for National Security was convened on Tuesday, attended by military commanders, intelligence heads and a representative from the president's office.
(ał/gs)
Source: IAR, PAP