(Reuters) - Slovak Prime Minister Robert Fico rejected protesters' calls for his resignation on Saturday after tens of thousands demonstrated against his government's policy shift closer to Russia.

Around 60,000 protested in the capital Bratislava on Friday, organisers estimated, and media said in total around 100,000 had turned out for rallies in cities across the country, the biggest demonstrations since Fico returned to power in 2023.

Protests were nearing levels seen in 2018 when the murder of an investigative journalist caused mass demonstrations and forced Fico's resignation during an earlier stint in office.

The latest protests come after Fico privately travelled to Moscow in December to meet Russian President Vladimir Putin, a rare encounter for a European Union leader since Russia invaded Ukraine in 2022.

"The government can only be changed if there are elections," Fico said in interview with the public broadcaster on Saturday when asked about the protests.

Fico's leftist-nationalist administration has accused progressive opponents this week of planning to escalate protests to try to overthrow the government illegally. Opposition parties and civic groups organising protests rejected the accusations.

Critics say the four-time prime minister's ruling coalition is weakening democratic values, while shifting foreign policy away from EU and NATO allies and closer to Russia.

The civic group Mier Ukrajine (Peace to Ukraine), which organised Friday's protests under the slogan "We are Europe", will hold more demonstrations on Feb. 7.

Fico has defended his government's foreign policy saying it seeks good ties with all sides, and while critical of some EU policies he has said policy was still determined by EU and NATO membership.

(Reporting by Jason Hovet in Prague)