Iran's supreme leader has mocked the U.S. presidential election, calling the tight race a "spectacle" that has exposed the weakness of democracy.

More than 24 hours after polls closed, several battleground states continue to count ballots, leaving the outcome of the race between President Donald Trump and Democratic challenger Joe Biden too close to call.

Trump has made unsubstantiated claims about fraud in the vote due to ongoing counting of mail-in ballots that has seen the president's lead in Michigan, Wisconsin, and other states slowly melt. Trump’s claims about fraud have even been condemned by many fellow Republicans.

Biden has said every American's vote will be counted and that his campaign will defend against legal challenges from the Trump campaign.

"What a spectacle!" Supreme Leader Ayatollah Ali Khamenei tweeted on late November 4.

"One says this is the most fraudulent election in US history. Who says that? The president who is currently in office," Khamenei said. "His rival says Trump intends to rig the election! This is how #USElections & US democracy are."

Earlier this week, Khamenei said the outcome of the election would have no impact on Iranian policy, although Trump and Biden would have different policies toward Tehran.

Trump unilaterally withdrew from the 2015 Iran nuclear deal and imposed crushing sanctions as part of his administration's "maximum pressure" campaign against the Islamic republic.

Biden has suggested he may rejoin the landmark nuclear agreement struck when he served as vice president under President Barack Obama.

Analysts say relations between Washington and Tehran will not only be determined by the U.S. elections.

Iran holds a presidential election in June 2021 in which incumbent President Hassan Rohani is ineligible to run after serving two terms. Rohani put much of his political capital on the embattled nuclear deal and has come under pressure from hard-liners over its failure.

The election could bring a hard-line candidate who is against any compromises or international nuclear deal to power.

Khamenei, 81, has final say on all matters in Iran.

Iran holds tightly controlled elections among carefully vetted candidates who come largely from the established political, military, and clerical establishment.

Following Iran's 2017 presidential election, hard-line presidential candidate Ebrahim Raisi, who is close to Khamenei, claimed there was widespread voter fraud when Rohani won.

An election dispute in Iran in 2009 triggered massive protests called known as the Green Movement, which were brutally put down by security forces.