Fico, who survived an assassination attempt last May, quoted from what he said was a classified report ahead of an opposition-sponsored motion of no-confidence in his government on Tuesday.

His claim coincided with a visit by Hungary’s prime minister, Viktor Orban.

Both leaders have strongly criticised Ukraine’s president and have advocated peace talks with Russia’s Vladimir Putin.

The opposition accused Fico of abusing the SIS to torpedo parliamentary procedure and prevent public scrutiny of his government, which holds a razor-thin majority.

Fico has warned of early elections if his coalition allies do not resolve their differences.

Tuesday’s no-confidence vote in the Slovak parliament was abandoned after the speaker agreed to Fico’s request to hold the entire session in secret.

The opposition promptly walked out.

Fico had insisted he would have to refer to the report – by Slovakia’s SIS civilian intelligence service – during the debate preceding the vote.

“The report was just a bunch of platitudes compiled from emails,” said Tomas Valasek, deputy leader of the liberal opposition Progressive Slovakia, which helped to file the no-confidence motion.

“But the act of classifying it was important, because it allowed them to classify the entire debate on the government’s failings,” he told the BBC from Bratislava.

“It was basically a procedural trick to muzzle the opposition. That’s all there is to the report,” he went on.

Speaking to reporters shortly after the debate, Fico accused the opposition of trying to overthrow his democratically elected government, a coalition of leftist, nationalist and populist parties.

“I can’t give you names and I can’t discuss the circumstances, but I can tell you in all seriousness that the Slovak opposition is planning a Maidan,” he said.

“The Slovak opposition is making plans to occupy government buildings. It intends to stop the authorities from carrying out their official duties,” the prime minister added.

The SIS later released a statement saying it had obtained serious information about a “long-term, organised influence operation with the aim of destabilising the Slovak Republic”.

The emails which allegedly featured in the classified report were later leaked to the daily SME newspaper.

Evidence of a secret coup plot looks thin.

The emails were from an NGO in the city of Banska Bystrica called “Not In Our Town”, which has been active since 2013. The emails do propose an escalating series of non-violent public protests and blockades of public buildings, with three stated goals:

• To force the government to act in accordance with the law and democratic principles
• To reject any form of collaboration with Russia and support Ukraine
• To maintain Slovakia’s pro-European and pro-Atlantic orientation.

But Not In Our Town said there was nothing secretive about the plans – they were written with the help of ChatGPT and were emailed to some 140 organisers.

“It is stressful, but on the other hand it’s rather ridiculous,” said one of the group’s coordinators called Martina, who preferred not to give her full name.

“We’ve put the emails on our Facebook page because there’s nothing secret about them. It’s crazy,” she told the BBC.

She had not, she said, been approached by the intelligence services.

The opposition has little faith in the impartiality of the SIS. One of Robert Fico’s first acts when he returned to office in 2023 was to appoint Pavol Gaspar, son of former police chief Tibor Gaspar, to run the agency.

Tibor Gaspar was forced to resign as chief of police following the murder of investigative journalist Jan Kuciak in 2018, a seismic event in Slovak politics that also forced Mr Fico to abandon his third term as prime minister.

Gaspar is now an MP in Fico’s leftist Smer party, and has just returned from a controversial visit to Moscow. His son says it is wrong to cast aspersions on the professionalism of the SIS.

Meanwhile, Fico will oversee an emergency session of the security council called for Thursday morning to discuss the findings of the “secret report”.

He promised “significant preventative measures” to prevent what he said was an alleged coup against his government.

He claimed that a group of US-funded experts involved in anti-Yanukovych protests in Ukraine and more recent demonstrations in Georgia, was already operating in Slovakia. It was being closely monitored by the Slovak intelligence services, he asserted.

Tens of thousands of Slovaks have demonstrated in recent months against the government’s alleged curtailing of the rule of law and media freedom, the renewal of relations with Russia and a halt in support for Ukraine.

The latest round of nationwide protests will be held on Friday.