A train driver reported irregularities on the Dęblin-Warsaw route early on Sunday near the village of Życzyn, about 100 km from the Polish capital, according to police in the central city of Radom.
Initial inspections showed part of the track had been damaged, police said.
Tusk said on X that he remained in constant contact with the interior minister about the incident.
"It cannot be ruled out that we are dealing with an act of sabotage," he wrote, adding that no one was injured and that security services were investigating.
Jacek Dobrzyński, spokesman for Poland’s security services, told the PAP news agency that police and the Internal Security Agency (ABW) were examining the circumstances and causes of the damage.
"The matter is being treated as an absolute priority," he said.
'Nothing can be ruled out': deputy interior minister
Deputy Interior Minister Maciej Duszczyk told broadcaster Polsat News that Poland "has faced many different acts of sabotage in recent months" and that Sunday's incident "may have been one of them."
He said authorities were not confirming reports that a blast had been heard, but added that the case was serious and would be investigated in detail.
"We have a damaged track, and it did not damage itself," Duszczyk said. "Someone must have caused it. Let the services establish how it was damaged, what tools were used, and then follow the full procedure."
He also cautioned against immediately blaming Russia.
"Russia is not so powerful that every fire or every incident is provoked by them," he said. "But nothing can be ruled out or ignored."
State rail carrier PKP Polskie Linie Kolejowe said the incident would be investigated by a railway commission and that repairs would begin once security services completed their work.
Earlier on Sunday, interior ministry spokeswoman Karolina Gałecka said investigators were working at the site under a prosecutor's supervision and that there were no initial indications the damage was deliberate.
(gs)
Source: PAP, IAR, TVP Info, TVN24