(Adds crowd estimate from phone operator in para 3)
By Michael Kahn
PRAGUE, June 23 (Reuters) - An estimated quarter of a million Czechs rallied in Prague on Sunday to demand the resignation of Prime Minister Andrej Babis, in the biggest show of public discontent since the 1989 Velvet Revolution which overthrew Communism.
The rally in Letna park was the culmination of a series of demonstrations in recent weeks against Babis, who has faced investigations over alleged fraud and conflicts of interest, claims he vehemently denies.
Organisers said they believed that about 250,000 people had attended Sunday's rally. Phone operator T-Mobile said its network usage analysis put the number of participants at over 258,000. A police spokesman declined to give an estimate.
The total population of the Czech Republic is 10.7 million.
Protesters carried banners saying "Resign", "We've had enough", "We won't give up democracy", and others waved Czech and EU flags. Many families brought children to the rally, which was peaceful as were other recent protests against both Babis and his justice minister.
Babis has said people have the right to protest but has firmly refused to step down. His populist ANO movement remains the most popular party, although its support has dipped slightly in the past two months to 27.5%, according to a poll by Kantar agency released on June 9.
Babis also has enough backing in parliament, where a no-confidence vote planned for Wednesday is likely to fail.
Police proposed in April that Babis, a billionaire businessman-turned-politician sometimes likened to U.S. President Donald Trump, should be formally charged for fraud in tapping a European Union subsidy a decade ago to build a hotel and conference centre outside Prague. He denies any wrongdoing.
The appointment of a new justice minister just after the police announcement prompted rallies by demonstrators suspicious that Babis was trying to influence proceedings. Babis has also vigorously denied that claim.
"Our country has many problems and the government is not solving them. It is not solving them because the only worry of the prime minister is how to untangle himself from his personal problems," said Mikulas Minar, a 26-year-old theology student who set up the Million Moments for Democracy, a civic group that organised the protests.
"It is unacceptable for our prime minister to be a person under criminal investigation," he told the crowd from a giant rock festival-like stage.
No politicians were invited to address the rally, the organisers said.
Filip Rubas, who joined protests in 1989 against the then communist regime, said he turned out on Sunday to send a message to politicians that they will be held accountable.
"We think our leaders need to be reminded very strongly that they do not own our country, that they are not above the law (or constitution) and that there are still enough caring people who are not brainwashed by hateful propaganda," said Rubas, 50.
He travelled to the rally with his wife and a group of friends from Brno, the country's second city, 200 km (125 miles) from Prague.
Babis, 64, suffered another setback from leaked preliminary results of an audit by the European Commission, which determined he is in conflict of interest as the beneficiary of trust funds where he had transferred his chemicals, farming, media and food business, valued at $3.7 billion by Forbes.
Babis insists the audit, which said companies in the trust fund should not be eligible for EU development subsidies, is wrong and this would be proven in the final conclusions, expected late this year or early in 2020. ($1 = 0.8798 euros) (Writing by by Jan Lopatka; Editing by Susan Fenton and Gareth Jones)
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