Gazeta Wyborcza daily reported in March that the phone of Jacek Karnowski was hacked using the software developed by Israel-based NSO Group in 2018-2019, when he was working on the opposition campaign for elections to the upper house of parliament, the Senate.

At the time Karnowski was mayor of the seaside resort of Sopot, a role he left after being elected to parliament on Sunday as part of a bloc of pro-European Union parties that are now poised to take power.

"I expect an investigative commission to be formed," Karnowski told Reuters. "I think this is realistic at the turn of the year."

In 2022 the opposition-controlled Senate created a commission to look into the phone-hacking allegations but it had no official investigative powers.

Karnowski said that senior officials including Prime Minister Mateusz Morawiecki and the leader of the ruling nationalist Law and Justice (PiS) party Jaroslaw Kaczynski should be called before the commission.

PiS has said that Poland has access to Pegasus, but has dismissed suggestions it was used against political opponents.

PiS came first in the election but is unlikely to be able to form a government for want of a coalition ally. The leaders of the three groupings that secured a combined majority have called on President Andrzej Duda, a PiS ally, not to delay appointing a new prime minister.

However, Duda's aides have said that he will not be rushed into making a decision.

(Reporting by Alan Charlish, additional reporting by Anna Wlodarczak-Semczuk and Pawel Florkiewicz)

By Alan Charlish