The Department of Homeland Security may also update the National Terrorism Advisory System to warn of a potential cyberattack from Iran, according to an official familiar with the discussions. The system’s bulletins, which are shared among law enforcement throughout the country, had not been updated with that information as of Friday night.

Lt. Cmdr. Scott McBride, a spokesman for the Coast Guard, said that “no known specific threats” to the nation’s ports had emerged to “warrant an increase in our operating posture.” There was also no indication from the Transportation Security Administration that airports were responding to a rising threat.

Typically, after an attack or threat is made against the United States, the Department of Homeland Security will host a call with leaders of the 50 states to share information and advise on security protocols. Information on potential threats or leads for investigations are shared through dozens of fusion centers that are partly funded by the department.

Homeland security also typically communicates with faith-based or community organizations that may be specifically targeted by a threat. Customs and Border Protection, an agency within the Department of Homeland Security, is responsible for vetting who enters and exits the country, in addition to patrolling the border.

The department also oversees the Cybersecurity and Infrastructure Security Agency, which will take the lead on communicating with the private sector to prevent a large-scale retaliation from Iran, current and former department officials said.

In his tweet, Mr. Krebs referred to a statement issued last summer from his agency warning of “a recent rise in malicious cyberactivity directed at United States industries and government agencies by Iranian regime actors and proxies.”

In that statement from June, Mr. Krebs said Iran did not just aim to steal data and money. “What might start as an account compromise, where you think you might just lose data, can quickly become a situation where you’ve lost your whole network,” he said.