Poland's former conservative nationalist Law and Justice (PiS) party government, which has since been voted out of office, is alleged to have spied on several hundred people using the Israeli software Pegasus.
The spy software was used to monitor 578 people between 2017 and 2023, according to a report for parliament published by the General Prosecutor's Office in Warsaw on Tuesday.
A parliamentary committee of inquiry is currently investigating whether the PiS government in office until December used Pegasus to spy on political opponents.
PiS leader Jarosław Kaczyński denied the spying allegations at the time.
According to reports in the Polish media, there are now indications that the PiS government also used the software to monitor prominent politicians from its own ranks.
Last week, Justice Minister Adam Bodnar announced that 31 people who had been the subject of attacks using Pegasus would be summoned by the public prosecutor's office to testify as witnesses.
Member of the European Parliament (MEP) Krzysztof Brejza later announced that he had received such a summons. Brejza is a member of Prime Minister Donald Tusk's liberal Civic Coalition (KO).
Before the 2019 parliamentary elections, he managed the election campaign of his party, which was part of the opposition at the time.
According to Polish media reports, in addition to Brejza, a female public prosecutor who had criticized the PiS government's judicial reforms and the prominent opposition lawyer Roman Giertych were also spied on using Pegasus.
Journalists, human rights organizations and data forensics experts first reported on Pegasus in July 2021.
Authoritarian governments around the world in particular had used the surveillance software on a large scale against critics, opposition activists and journalists, the reports said at the time.
Pegasus uses security vulnerabilities in smartphones to gain far-reaching access to data. It can also be used to eavesdrop on conversations.