"I am ready to do whatever it takes to give the republic back to the people," he told a local television station, Markiza.
He said he wanted to prevent the return to power after 2020 of Slovakia’s long-ruling Direction party in a coalition with People’s Party.
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Kiska backed Zuzana Caputova, a lawyer and civic activist, in last month’s presidential election. He called her election a victory and urged opposition parties to unite.