LONDON — Hungary’s leader issued a blistering attack against the American billionaire and philanthropist George Soros on Wednesday, after the European Union criticized a new Hungarian law that threatens to shut a university founded by Mr. Soros.

“I know that the power, size and weight of Hungary is much smaller than that of the financial speculator, George Soros, who is now attacking Hungary,” Prime Minister Viktor Orban told members of the European Parliament in Brussels, in a sarcastic but methodical speech. He called Mr. Soros “an open enemy of the euro,” a reference to the role currency speculation played in building Mr. Soros’s fortune.

It was an exceptional attack by a head of government against a private citizen, albeit a wealthy and powerful one. Mr. Soros has been a frequent target of criticism from right-wing news media organizations like Breitbart and Infowars, which deplore his affinity for Democratic and liberal causes. Supporters of Mr. Soros, who is 86, a native of Hungary and a Holocaust survivor, have detected a whiff of anti-Semitism in the attacks in the United States.

In 1991, after the fall of Communism, Mr. Soros founded Central European University, which is based in Budapest and accredited in Hungary and the United States. A law recently rushed through Hungary’s Parliament would force the university to close if it did not open an American campus.