Czech police said on Saturday they were investigating an anonymous threatening letter against presidential candidate Andrej Babiš.
The letter contained live ammunition and explicit insults, Babiš told Czech news agency CTK.
Babiš, a billionaire who founded the centre-right populist ANO 2011 (Action of Dissatisfied Citizens 2011) political party, said such threats against a political candidate and his family should have no place in a free society.
Babiš is facing independent politician Petr Pavel, a retired army general and former top NATO official, in the run-off election for Czech president next weekend.
Pavel condemned the threats against Babiš alongside other top Czech politicians.
In the Czech Republic, a parliamentary democracy, the president serves as head of state and holds largely ceremonial powers.
Polls currently favour Pavel in the election, although observers still consider Babiš a viable candidate.
Babiš in his campaign has prominently criticized Pavel’s support for weapons deliveries to Ukraine, arguing such explicit support risks drawing the Czech Republic into a war with Russia.
Babiš instead has said he would like to mediate peace talks between Ukraine and Russia in Prague if elected.