"I do not support invoking the Insurrection Act," Esper said, two days after President Donald Trump said he could do so to call up the army to quash protests.

"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," Esper said.

"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," he told reporters in the Pentagon.

"We are not in one of those situations now."