US President Donald Trump held a Nevada campaign rally at an indoor venue on Sunday despite public health professionals' warnings against large indoor gatherings during the coronavirus pandemic.

Iran PressAmerica: Donald Trump, a Republican, railed against his Democratic rival, former Vice President Joe Biden, suggesting he was taking drugs and was soft on crime, Reuters reported.

"Biden wants to appease domestic terrorists and my plan is to arrest domestic terrorists," Trump said to an enthusiastic crowd. "If Biden wins, the mob wins."

People in the crowd were seated close together and many did not wear masks.

Biden has criticized Trump for holding campaign events that put people at risk of contracting the coronavirus, which has killed more than 194,000 people in the United States.

Trump played down the virus in its early stages and has alternately embraced and disregarded advice from public health experts, who encourage mask-wearing and maintaining social distance to prevent its spread.

The president's campaign portrayed the rally at a large warehouse in Henderson as an opportunity for supporters to exercise their rights to peaceful assembly under the US Constitution's First Amendment.

"If you can join tens of thousands of people protesting in the streets, gamble in a casino, or burn down small businesses in riots, you can gather peacefully under the First Amendment to hear from the president of the United States," spokesman Tim Murtaugh said in a statement.

Participants were to have temperatures taken before entry and be given a mask they would be encouraged to wear, the campaign said.

"I think we're relatively safe here. I brought a mask but I haven't felt the need to wear it," said Ronda Livingston, 64. "I'm not worried about it."

Trump, who is trailing Biden in national polls and in Nevada, has stepped up the frequency of his rallies in recent weeks but has held most of them at outdoor venues or in large open airplane hangars to help minimize risk.

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