Police are conducting raids in eastern Slovakia on houses linked to members of Italian mafia, after it emerged a journalist was writing a story about them before he was shot dead last week.
The country's police chief, Tibor Gaspar, told reporters in the eastern town of Michalovce that about 10 people should be detained.
Slovakian media reported that one of the detained was Antonino Vadala, an Italian who conducted business with at least two officials close to Prime Minister Robert Fico.
The officials resigned from their posts in the government office on Wednesday.
The bodies of 27-year-old Jan Kuciak and his girlfriend, Martina Kusnirova, were found on Sunday evening in their house in Velka Maca, east of the capital, Bratislava.
Mr Kuciak's last, unfinished story was about the activities of the Italian 'Ndrangheta syndicate in Slovakia.