The US presidential elections were "tarnished" by legal uncertainty and attempts to undermine public trust in the process, said international observers from the Organisation for Security and Co-operation in Europe (OSCE).
The international election observers said that the US election was "well managed despite the many challenges caused by the COVID-19 pandemic."
The international mission said however that "the campaign was characterised by deeply entrenched political polarisation that often obscured the broader policy debate and included baseless allegations of systematic fraud."
Michael Georg Link, leader of the short-term OSCE observer mission, said Donald Trump's allegations of deficiencies "harm public trust in democratic institutions".
Trump attempted to cast doubt on the vote tallies that continued throughout the day on Wednesday, accusing states of "surprise ballot dumps" as states counted absentee and mail-in ballots from drop boxes across crucial battleground states.
The president also called into question the "integrity" of the process, although election officials said the day went well.
Wisconsin elections commissioner Meagan Wolfe said nothing about the day was a surprise to her and election officials had given their "hearts and souls".
Wolfe said that she felt "so confident that every single valid ballot was counted in the state of Wisconsin".
"I think that we should feel really proud about the election that was conducted yesterday," Wolfe said.
Biden was projected to win the battleground state of Wisconsin with some 20,500 votes. The Trump campaign has said it will likely ask for a recount in the state.
The OSCE said the pandemic was a challenge but election day was peaceful. The mission sent 102 observers from 39 countries to the US.
Observers said that voter identification requirements disenfranchised certain groups of people and that campaign finance remains an issue in the US. The total expenditure is estimated to reach $14 billion (€11.8 billion) for these elections, the OSCE said.
"While the United States has taken great strides toward expanding the franchise, concerns remain regarding universal adult suffrage," said Kari Henriksen, head of the OSCE parliamentary assembly delegation.
"In the context of COVID-19 and the rise in mail-in voting, I am concerned about attempts to restrict the counting of legally cast ballots," Henriksen added.
Election officials worked under tough circumstances in the US due to a polarised climate as well. Though counting can be publicly observed, some armed protesters showed up in Arizona outside the election offices.
"While emergency funds were distributed to help states overcome challenges caused by the pandemic for the organisation of the elections, these were insufficient to overcome the additional challenge of the massive increase in online voter registration and postal voting," the OSCE said in a statement.
Biden has already broken the record for the most votes won by a US candidate, breaking Barack Obama's 2008 record. Turnout was also set to be much higher than any recent elections.