WARSAW (Reuters) - Poland's domestic security agency is investigating a hacking attack on the country's railway network which led to traffic disruption overnight, the state-run Polish Press Agency reported on Saturday.

Poland's Internal Security Agency (ABW) and police are probing an unauthorized use of the system involved in rail traffic management, Stanisław Zaryn, deputy coordinator of special services, told the news agency.

Hackers used railway frequencies to transmit a signal that triggered an emergency stoppage of trains in northwestern Poland causing delays, the agency reported.

Zaryn said any such interference was treated seriously given recent attempts by Russia to destabilize Poland.

"Such attempts are being made by the Russian Federation in cooperation with Belarus, and also for this reason we do not underestimate any signals that come to the ABW," he said.

Separately, the state railway operator is investigating the derailment of two trains and a collision of another two on Thursday. No one was injured in these incidents.

According to Zaryn, there was currently no indication that Thursday's incidents were linked with the hacking attack.

(Reporting by Marek Strzelecki; editing by Christina Fincher)