Jacek Dobrzyński, spokesman for the government minister overseeing Poland's security services, told reporters that the case is "dynamic and developing," and that he could not yet disclose details.
But he said more detentions were likely.
"I can confirm that the first detentions are already taking place. Individuals involved are being detained by the Internal Security Agency and by the police," Dobrzyński said.
"Several people have been detained. They are now being questioned, and investigators are determining the role each person played in this terrorist attack," he added
He said the arrests were made in Poland and that investigators had secured "a significant amount of evidence."
He added that the operation was being treated as a top priority, with officers from the Central Bureau of Police Investigation, the Internal Security Agency (ABW) and top prosecutors working on the case.
Dobrzyński urged caution in releasing information to the public, warning that Russian intelligence agencies were "monitoring the situation closely."
Jacek Dobrzyński. Photo: PAP/Piotr Nowak
"We cannot relay unverified information or speculate," he said. "Russian security services want to know exactly which direction Polish services and the police are pursuing."
Two sabotage attempts were reported over the weekend on the Warsaw-Dorohusk line, a key route for transporting Western aid to Ukraine.
In the first incident, an explosive device destroyed a section of track near the village of Mika.
In the second, a train carrying 475 passengers was forced into an emergency stop near the Gołąb station after damage to rail infrastructure was detected.
On Tuesday, Prime Minister Donald Tusk told parliament that authorities had identified two Ukrainian citizens working with Russian intelligence as suspects in the attacks.
The men fled Poland shortly after the incidents, he said.
A special meeting of the government’s security committee was held on Tuesday with senior military commanders, intelligence chiefs and a representative of the president.
(gs)
Source: IAR, PAP