The statement from the State Department came hours after Venezuelan media reported intimidation attempts on Guaido's convoy of vehicles Tuesday night.
"The United States condemns the attacks on Interim President Juan Guaido's caravan and the harassment of National Assembly deputies and members of the media," the State Department said in a statement Tuesday, adding that it is monitoring the use of armed intimidation gangs affiliated with Maduro.
At a meeting Wednesday at the White House with President Donald Trump, Guaido's wife, Fabiana Rosales, addressed her husband's safety. Rosales left Venezuela with her young child earlier this month amid safety concerns. She has previously traveled and met presidents of Peru and Chile.
"I fear for my husband's life. Yesterday, his life was attacked," Rosales said. "Also, his chief of staff, Roberto Marrero, was kidnapped in a very violent and vile manner. Not only is he his chief of staff, he is a personal friend."
The U.S. is among the countries that recognize Guaido, leader of the Venezuelan National Assembly, as the nation's interim president.
"Venezuela was and is still a country with tremendous potential where people are starving," Trump said. "They're getting killed. They're being beaten. What's going on there is unfathomable."
On Wednesday, Guaido asked people at a demonstration to trust their capacity to overthrow Maduro's regime, even without international support.
"You need trust yourselves that we can do it. It depends on us, otherwise we would only have to sit back and wait for somebody else," he said. He reiterated his offers of amnesty for the military to stop supporting Maduro, according to a video Guaido shared on Twitter.
Aid will soon arrive to Venezuela through a new Operation Freedom, he added.
The U.S. was one of the first countries to recognize Guaido after he declared himself interim president based on Venezuelan laws allowing the head of National Assembly to take over the presidency if it is declared vacant. The National Assembly previously declared Maduro's re-election illegal, on grounds the opposition was not represented in a 2018 vote.