De Blasio laid out the security plan with NYPD Commissioner Dermot Shea and Deputy Commissioner John Miller hours after USA missiles struck and killed a top Iranian military commander, Gen. Qassem Soleimani, at the Baghdad airport.
Iran told the United States that there would be a "harsh retaliation" for the death of Gen. Qassem Soleimani, who was head of Iran's elite Quds Force.
The demonstration held in Pershing Square came in response to the recent USA killing of a top Iranian commander in Baghdad, which has increased tensions between the United States and Iran.
"At this time there is no specific, credible threat against the homeland".
The city is constantly vigilant against possible terrorist attacks given its history, but de Blasio said the threat changed significantly overnight considering the resources of a modern, major nation such as Iran compared to those of non-state organizations like al Qaeda or ISIS.
It added that Tehran maintains a "robust cyberprogram and can execute cyberattacks against the United States".
Mayor de Blasio shared a tweet, which said, "Have spoken with Commissioner Shea + Dep Commissioner Miller about immediate steps NYPD will take to protect key NYC locations from any attempt by Iran or its terrorist allies to retaliate against America".
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There were protests planned in more than 70 USA cities Saturday, organized by the Act Now to Stop War and End Racism Coalition, with demonstrators chanting anti-war slogans and carrying signs reading, "no war or sanctions on Iran!"
The website of the Federal Depository Library Program was replaced with a page headlined with "Iranian Hackers!" displaying images of Iran's supreme leader, Ayatollah Ali Khamenei, along with the Iranian flag.
"There are opportunities for them to cause real disruption and destruction", John Hultquist, director of intelligence analysis at the cybersecurity firm FireEye, told AP.
As Iran threatened retaliation against the United States, local officials said there was no imminent danger in Southern California, but they would remain vigilant.
The U.S. Department of Homeland Security (DHS) warned in a terrorism threat alert issued through the National Terrorism Advisory System (NTAS) that potential cyberattacks carried out by Iranian-backed actors against the U.S. have the potential to disrupt critical infrastructure.
"My worst-case scenario is a municipality or a cooperative-type attack where power is lost to a city or a couple of neighborhoods", Lee told AP.