Tens of thousands of Slovaks have rallied to demand the resignation of prime minister Robert Fico’s government following the murder of a journalist that has shocked the central European nation and stoked anger over sleaze in public life.

Ján Kuciak and his fiancee, Martina Kušnírová, both 27, were found shot dead at their home near Bratislava on 25 February. Police have said Kuciak’s death was “most likely” related to an investigation of his that resulted in an article on alleged ties between Slovakia’s top politicians and the Italian mafia, which his employer posthumously published.

Slovak media called Friday’s protest in the capital, Bratislava, the biggest since the 1989 Velvet revolution that toppled communism in Czechoslovakia. Thousands marched in other Slovak cities, while hundreds of people gathered in cities in Europe and elsewhere.

Organisers demanded a thorough investigation of Kuciak’s death and a “new trustworthy government”. “Politicians in power have lost our trust,” said protester Maria Kuliovska, a 30-year-old mother on maternity leave. “We don’t trust them to guarantee an independent investigation. They have failed to investigate all previous scandals.”

Kuciak’s journalism and then his murder have rekindled public frustration with the government’s failure to tackle graft and cronyism in Slovakia nearly three decades after the fall of communism and 14 years after it joined the European Union.

Fico has led the country of 5.4 million people for 10 of the last 12 years and the economy has flourished, but the protesters in the capital, Bratislava, on Friday – estimated at up to 50,000 by the public broadcaster – chanted “Enough of Fico” and jangled keys just as they did in 1989 anti-communist rallies.

President Andrej Kiska, a political rival of Fico, has said Slovakia is suffering a crisis of trust and has called for a revamp of the three-party coalition or an early election.

Kiska, Fico and parliamentary speaker Andrej Danko – the country’s three highest officials – failed to agree a planned written declaration to help defuse tensions in talks on Friday.

After their meeting, flanked by the president and prime minister, Danko read a brief statement: “We want society to remain peaceful and calm and [Slovakia’s] top three officials will do their best to prevent the events of recent days from being politically exploited.”

Police and state officials, including Fico, had warned of potential violence at demonstrations, though there were no reports of disruption.

Fico has accused foreign forces of trying to destabilise Slovakia and has questioned the president’s meetings with financier George Soros in New York last year without any foreign ministry official being present.

The attack on the Hungarian-born billionaire echoes those of Hungary’s prime minister, Viktor Orbán, who hasaccused Soros of interfering in Hungarian politics.

Fico said he would meet his two coalition partners at the weekend to seek a deal to keep the government in place. He has resisted a call from the inter-ethnic Most-Hid party to sack interior minister Robert Kaliňák, his close ally.

Some analysts say Fico’s coalition could break up, although he might be able to continue leading a minority government with the backing of a far-right party in parliament.

Martin Slosiarik, an analyst at Focus polling agency, said Fico had never faced a crisis on this scale. “Kuciak’s last story has had a serious impact on people’s trust in the system of government, and the murder of two young people has added a strong moral aspect,” he said.