Hillary Clinton has criticised Tory MEPs for opposing an EU censure of Hungary over alleged attacks on the media, minorities and the rule of law.
The European Parliament last month approved disciplinary action against Viktor Orban’s government, which denies its actions breached EU “core values”.
Conservatives voted against the motion, saying they did not want to interfere with Hungary’s “internal democracy”.
But former US First Lady Mrs Clinton called the decision “disheartening”.
The 2016 Democratic presidential candidate has been marking the 70th anniversary of the Universal Declaration of Human Rights at the Bonavero Institute of Human Rights at the University of Oxford.
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In a wide-ranging speech on Tuesday, Mrs Clinton said: “It’s disheartening to watch conservatives in Brussels vote to shield Viktor Orban from censure, including British Tories.
“They have come a long way since the days of Margaret Thatcher and Winston Churchill.”
Since coming to power, Mr Orban’s government has taken a hardline stance against immigration, making it a criminal offence for lawyers and activists to help asylum seekers.
It prompted two-thirds of the European Parliament to back disciplinary action, amid reports of pressure being put on Hungary’s courts and electoral system.
British Conservative MEPs supported the Hungarian government, arguing that the EU had intruded into purely national matters.
Afterwards, Environment Secretary Michael Gove told the BBC it did not amount to an endorsement of Mr Orban, saying the MEPs were observing a “long-standing principle” on sovereignty.
In her speech Mrs Clinton described Hungary’s democracy as a “masquerade”, saying “illiberal democracy is a contradiction in terms”.
“Democracy also requires free expression and a free press, the rule of law and an independent judiciary. Without these things illiberal democracy is no democracy at all, it is just authoritarianism by another name.”
On Monday, Mrs Clinton unveiled a statue at the Bonavero Institute honouring wartime US First Lady Eleanor Roosevelt’s championing of human rights.