US President Donald Trump has warned his fellow Republicans their opponents may “steal” November’s election, as his party anointed him as their candidate.
“They’re using Covid to defraud the American people,” Mr Trump told delegates on the first day of the party convention in North Carolina.
Mr Trump repeated his much-disputed claims that mail-in ballots could lead to voter fraud.
Opinion polls suggest he is lagging behind Democratic challenger Joe Biden.
Mr Biden, the former vice-president to Barack Obama, has boasted a 10-point lead on occasions.
Addressing delegates in person at a party conference that has been dramatically scaled back by Covid-19, Mr Trump accused Democrats of “using Covid to steal an election”.
The US president has repeatedly suggested an unprecedented surge in postal voting could lead to widespread fraud even though experts and voting officials say this is a false conspiracy theory.
“The only way they can take this election away from us is if this is a rigged election,” he said. “We’re going to win.”
Mr Trump had also warned of a “rigged” election in 2016, as he trailed Hillary Clinton in the polls.
But in 2016 the polls were far less clear and just a few percentage points separated Mr Trump and his then-rival Hillary Clinton at several points as election day neared.
On Monday, Mr Trump was officially nominated as a formality to be the Republican nominee at his party’s convention in the city of Charlotte.
Supporters cheered him, chanting: “Four more years!”
The president is expected to make live television addresses on every day of the convention, leading up to his acceptance speech to the party jamboree on Thursday. It is unusual for candidates to address the convention before that point, as Mr Trump has done.