Image source, ReutersImage caption, President Zeman is "incapable" of fulfilling his duties, the head of the senate says
Czech Prime Minister Andrej Babis has called on the head of the president's office to resign immediately over alleged impropriety in exercising the powers of ailing President Milos Zeman.
Police are investigating allegations of "criminal acts against the republic".
President Zeman is currently in intensive care in hospital.
He was admitted a day after elections in which the centre-right opposition effectively ended Mr Babis's chances of remaining in power.
Now Czech politics have been thrown into turmoil by bombshell revelations by Senate Chairman Milos Vystrcil.
For over a week, the president's office has insisted Mr Zeman's undisclosed illness does not prevent him from fulfilling his constitutional obligations.
However, the head of the senate says he has received official confirmation from the director of Prague's Central Military Hospital that the president is "incapable of fulfilling any of his working responsibilities" – in other words unable to carry out his duties.
Image source, Getty ImagesImage caption, President Zeman was admitted to this hospital in Prague the day after Czech elections
The role of the Czech head of state is a largely ceremonial one, but that role swells in importance after an election: it is the president who asks someone to form a new government.
He also accepts the resignation of outgoing prime ministers, and convenes parliament.
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Mr Zeman's indisposition, therefore, casts the smooth running of that process into doubt.
Particular attention is now being paid to a meeting on 14 October, when President Zeman's senior aide, Vratislav Mynar, escorted lower house chair Radek Vondracek to see Mr Zeman – a lifelong chain-smoker and heavy drinker – in an ICU unit.
Mr Vondracek's brief visit was not approved by the hospital director, who is also Mr Zeman's personal doctor. But he emerged with a letter bearing the president's signature reconvening parliament on 8 November.
The head of the senate says the hospital had informed Mr Mynar on 13 October that President Zeman was wholly unfit to work.
Police are now investigating the circumstances of that meeting – including possible "crimes against the republic", which in the Czech criminal code include such offences as subversion, sabotage and treason.
They are even investigating allegations that the president's signature on the letter was forged.
There is also serious political fallout.
Mr Babis – who until now has been locked into an uneasy alliance with President Zeman – has called on Mr Mynar to resign immediately from his post as head of the president's office.
Image source, ReutersImage caption, Prime Minister Andrej Babis has called on the head of Mr Zeman's presidential office to resign
If not, he says, he will sack him using presidential powers that will be granted to him if parliament relieves Mr Zeman of his duties by triggering article 66 of the Czech constitution.
However, this cannot happen at least until 8 November, when the newly elected lower house sits for the first time.
The prime minister has also criticised Mr Vondracek, a member of his ANO party, saying he had been used as a "useful idiot" by Mr Mynar.
Meanwhile, there is still no news of the 77-year-old president's exact diagnosis.
His personal doctor says patient confidentiality means all he can say is that Mr Zeman is being treated for complications arising from his chronic conditions, which in his case is Type 2 diabetes and neuropathy in his lower limbs.
Widespread reports in the Czech media, including one backed up by seven independent sources familiar with his health, say he is suffering from serious complications from cirrhosis of the liver.
Those complications, claim the reports, include a build-up of abdominal fluid known as ascites and also hepatic encephalopathy, which can affect cognitive function.
The president's office has not commented on those claims, instead thanking those who have wished the president a speedy recovery and urging them to continue praying for him.
The hospital report quoted by the senate chairman, however, says President Zeman's prognosis is "extremely unclear" and his return to work in the weeks to come is "highly unlikely".