Slovenia's conservative prime minister congratulated US President Donald Trump on Wednesday for winning re-election even though neither Trump nor challenger Joe Biden has yet won an outright victory.

"It's pretty clear that American people have elected Donald Trump and Mike Pence for four more years," Janez Jansa -- whose country is First Lady Melania Trump's homeland -- wrote on Twitter.

"More delays and facts denying from MSM (mainstream media), bigger the final triumph for POTUS," he said.

Trump himself declared victory on Wednesday despite results in several states yet to be called, and urged the Supreme Court to stop vote counting over what he alleged was "major fraud".

Jansa, leader of the anti-migrant Slovenian Democratic Party (SDS), has been accused by Slovenia's opposition and mainstream media of using the coronavirus crisis to attack independent and critical media.

Jansa, along with Hungary's Prime Minister Victor Orban, was one of the few European Union leaders to endorse Trump's candidacy, and he said Biden would be "one of the weakest US presidents in history".