In Bratislava, the capital, protesters waving Slovak and European Union flags shouted "Enough of Fico" as they gathered in Freedom Square, located near government buildings, to oppose changes sought by a government appointed in October.

"I believe, friends, it is not self-confidence and certainty that is being felt in the government. It is panic and fear that we will stop them," Michal Simecka, head of the biggest opposition party in parliament, Progressive Slovakia, told the crowd as he promised to fight against passing the bills.

Protesters also gathered in other cities across the European Union nation of 5.4 million, including Nitra, Banska Bystrica and Kosice.

Fico's government aims to approve legislation by Christmas that would disband as soon as in January the special prosecutor's office (USP) that has been in place for two decades to battle graft and organised crime.

Slovak President Zuzana Caputova has said the proposed changes included unacceptable political meddling in personnel matters and said they threaten to weaken the position of whistle-blowers and could lead to a halt in the inflow of European Union funds.

The European Commission, which has clashed with EU members Poland and Hungary in the past over rule-of-law issues, has urged Slovakia not to make hasty changes, a call joined by the United States.

Fico, who resigned as premier in 2018 amid mass protests against corruption that followed the murder of an investigative journalist, leads a coalition with a sufficient majority in parliament to overturn a presidential veto. He has accused the special prosecutor's office of being politically motivated and has said its actions violated human rights.

Since the 2020 victory of another anti-Fico government coalition, the USP has investigated over 100 people including police and judicial officials and influential businessmen, and around another 40 have been sentenced, according to Slovak media.

(Writing and additional reporting by Michael Kahn in Prague; Editing by Leslie Adler)

By Radovan Stoklasa