White House National Security Advisor Jake Sullivan. AFP
"Make no mistake: the United States of America will protect and defend its citizens," White House National Security Advisor Jake Sullivan said in a statement.
"Should Iran attack any of our nationals, including any of the 52 people named yesterday, it will face severe consequences."
The Islamic republic on Saturday announced the sanctions, including on US Chairman of the Joint Chiefs of Staff Mark Milley, for their role in the death of Qassem Soleimani, a powerful Iranian commander.
Soleimani, leader of the Iranian Revolutionary Guards' Quds Force, was killed by a US drone strike in Baghdad on January 3, 2020, in what Iran on Saturday called a "callous terrorist act."
Days ago Iran's President Ebrahim Raisi vowed revenge against Donald Trump unless the former US president is tried over Soleimani's killing, as Tehran marked two years since the revered commander's death.
In addition to Milley, the sanctioned Americans include Trump-era national security advisor Robert O'Brien and Nikki Haley, who served as US envoy to the United Nations.
"Looks like I'll have to cancel my relaxing getaway to Iran," tweeted Haley.
"When you get sanctioned by Iran, the world's leading state sponsor of terror, you know you're doing something right."
Sullivan in his statement said that while Americans have disagreements on politics and on Iran policy, "we are united in our resolve against threats and provocations (and) we are united in the defense of our people."
The United States, he added, will work with allies "to deter and respond to any attacks carried out by Iran."
Washington and other world powers are currently engaged in closed-door talks with Iran in Vienna aimed at reviving a 2015 nuclear deal that was mothballed in 2018 when Trump pulled the United States out of the agreement and slapped punishing sanctions on the regime.