Vance's remarks came during a visit to Budapest aimed at boosting the chances of the nationalist Orban, who faces the toughest challenge of his 16-year rule in an April 12 election seen as crucial for the influence of supporters of Donald Trump's MAGA movement in Europe.
Hungary's strained relations with Ukraine have taken centre stage in the election campaign, with Budapest accusing Kyiv of deliberately stopping flows of Russian oil through the Druzhba pipeline in an effort to sway the ballot.
Hungary responded by blocking a 90 billion-euro ($A149 billion) EU loan for Ukraine, prompting Ukrainian President Volodymyr Zelenskiy to say he could give the address of whoever was responsible to the Ukrainian army, who could "speak with him in their own language".
Speaking at a Hungarian university, Vance said Orban had told him about Zelenskiy's remarks.
"It's completely scandalous," Vance said on Wednesday.
"You should never have a foreign head of government ... threatening the head of government of an allied nation."
Vance then accused the media of double standards in their coverage of alleged foreign interference in the 2016 US presidential election and in the Hungarian vote.
"You saw this back in 2016 where a lot of the American media said that it was a true scandal that the Russian government bought like $US500,000 of Facebook advertisements ...That's foreign influence," he said.
"But what's not foreign influence is when the European Union threatens billions of dollars withheld from Hungary because you guys protect your borders ... What's not foreign influence is when the Ukrainians shut down pipelines, causing suffering among the Hungarian people in an effort to influence an election."
Budapest has been embroiled in a long-running dispute with the European Union over issues ranging from judicial independence to the treatment of migrants.
