From the White House podium, Sarah Sanders also took aim at the regime, accusing it of spending Iran's "wealth on spreading militancy and terror overseas, rather than ensuring prosperity at home".
The brutal regime has moved to squash the burgeoning protests by cutting off communication, which it did successfully almost nine years ago. The protests appear to remain leaderless.
The protests began on December 28, sparked by Iran's flagging economy and a rise in food prices, before morphing over the following days into calls for the downfall of Iran's theocratic government.
Protests began in Iran's second largest city Mashhad and quickly spread to become the biggest challenge to the Islamic regime since mass demonstrations in 2009. Most of the casualties among protesters have occurred in those regions.
State TV described the rally as a "response to rioters and supporters of the riots".
"That is why we are working to deter violence on behalf of the regime against the peaceful protesters, and to take other measures such as rousing global support to try to prevent a brutal crackdown by the regime", Peek said.
President Trump tweeted, "The U.S.is watching".
"In recent days, enemies of Iran used different tools including cash, weapons, politics and intelligence services to create troubles for the Islamic Republic", said Khamenei, whose powers exceed those of the elected president, Hassan Rouhani.
Wednesday also saw the arrest of a European citizen, who was detained in the west of the country under accusations of foreign meddling, but whose nationality has not been specified.
"We no longer consider them as protesters demanding rights, but as people targeting the regime", he told the conservative Tasnim news agency. Some pro-government demonstrators carried signs showing Trump's face covered with a bright red "X".
President Trump has made several statements of support for the protesters.
Anti-regime protests in Iran erupted again Tuesday, prompting a crackdown by government forces that left nine more people dead, according to Iranian state media. Prior to Trump's latest tweet, Iran's Foreign Ministry spokesperson Bahram Qassemi condemned the USA president's previous "absurd and insulting" comments. Twitter and Facebook were already banned.
The authorities have also blocked two popular social media apps - Telegram and Instagram - as a security measure.
Will vocal US calls for democracy in Iran help the cause of the dissidents or, as critics fear, allow the mullahs in Tehran to blame the unrest on the USA and, of course, Israel?
Los Angeles grocer Todd Khodadadi says Iranians are "trying to get their rights, and they raised their voices..." The offense carries a death penalty in Iran. Zeid Ra'ad Al Hussein also asked Iran to allow the people to be heard and to have the right to peaceful demonstrations, and that no further life should be lost.
An activist video meanwhile showed unrest in Noor Abad, in Lorestan province, some 360 kilometers (225 miles) southwest of Tehran. They later set fire to an ambulance in anger over what they describe as the local hospital's refusal to treat their wounded.