Donald Tusk made the statement in a media interview on Friday evening.
The prime minister was asked about President Andrzej Duda's announcement that he would pardon Poland's ex-interior minister Mariusz Kamiński and his former deputy Maciej Wąsik, who were jailed on Tuesday for abuse of power while in charge of Poland's anti-corruption service CBA in 2007.
Tusk said he had "no comment to make" as a pardon was the prerogative of the president, not the prime minister.
The prime minister said that "the crucial thing is that Poland restores the rule of law, so that officials act according to their prerogatives."
Tusk said Kamiński and Wąsik had been convicted of abuse of power and so lost their MPs' mandates and had to be taken to prison, in line with the law.
The prime minister said that the previous government led by the Law and Justice (PiS) party, and the president as its ally, "destroyed the independence of the courts and the prosecution service" as well as "the rule of law in Poland."
Tusk stated that his Cabinet would ensure "the prosecution office will be independent in its opinions and actions."
"Together we must defend the rule of law," the prime minister added.
He stressed that officials must "perform duties dictated by law, not by politicians."
Tusk also said in the interview he would meet with the president on Monday for talks on "security issues, support for Ukraine and internal matters," polskieradio24.pl reported.
In 2015, Mariusz Kamiński and Maciej Wąsik were sentenced to 3 years in prison for abuse of power when in charge of CBA in 2007.
Later the same year, the president pardoned the two officials.
In June 2023, Poland's Supreme Court said the case should be reopened as the president's pardon was improper, because it was issued before the two were finally convicted.
In December 2023, the district court in Warsaw sentenced Mariusz Kamiński and Maciej Wąsik to two years in prison.
Police on Tuesday detained the two ex-ministers and they were taken to prison to serve their sentence, polskieradio24.pl reported.
Source: Polish Radio, polskieradio24.pl, Polsat News