US Defence Secretary Mark Esper on Wednesday said he opposed invoking a rarely used law to send in the military to quell nationwide protests over police brutality against African Americans.
Two days earlier, President Donald Trump said he could invoke the law from 1807 to send in the army.
"I do not support invoking the Insurrection Act," Mr Esper said.
"I've always believed and continue to believe that the National Guard is best suited for performing domestic support to civil authorities in these situations.
"The option to use active-duty forces should only be used as a matter of last resort and only in the most urgent and dire of situations.
"We are not in one of those situations now."
On Monday, Mr Trump threatened to send in the military even if state governors rejected the move.
“If a city or state refuses to take the actions that are necessary to defend the life and property of their residents, then I will deploy the United States military and quickly solve the problem for them," he said.
His comments sparked wider protests in Washington and other US cities for the second week in a row over the killing of a black man, George Floyd, by the police in Minneapolis.
Pope Francis on Wednesday decried racism and violence in the US.
“We cannot tolerate or turn a blind eye to racism," he said.
The pope said he would pray for the "repose of the soul of George Floyd and of all those others who have lost their lives as a result of the sin of racism".
But he also condemned the violence that followed as "self-destructive and self-defeating”.
“Nothing is gained by violence and so much is lost,” Pope Francis said.
Protests continued across the US but have been mostly peaceful in cities including Portland, Washington, and San Francisco.
Looting continued in New York City but to a lesser extent than previous days.
Former US president Barack Obama was due to address the nation on Wednesday afternoon about Mr Floyd’s death.
In 2008, Mr Obama made history as the first African American to be elected president.
Ella Jones became the first African-American and first woman to be elected mayor of Ferguson, Missouri, on Tuesday.
Ms Jones's victory, alongside the protests, came six years after the city saw the killing by police of a black teenager, Michael Brown.
That tragedy gave the Black Lives Matter movement its broad national appeal. Ms Jones took 54 per cent of the vote.
In Iowa on Tuesday night, right-wing Congressman Steve King, the nine-term representative, was defeated in a primary challenge for Republican party candidacy.
Mr King is known for his anti-immigrant and anti-Muslim speech.
In an interview with Breitbart, he attacked Muslims for not eating pork. And in 2018, he compared immigrants to "dirt".
His defeat and Ms Jones' win show both parties have cracked down on racism, five months before the general election between Mr Trump and his Democratic rival Joe Biden.