The bulletin issued on Saturday, which the agency said describes "current developments or general trends regarding threats of terrorism," came after a US airstrike in Iraq on Friday that killed senior Iranian commander Qassem Soleimani.

Citing Iran's public statements that it intends to retaliate against the United States, the bulletin said there is no information at this time "indicating a specific, credible threat" to the US homeland.

The bulletin claimed Iran "maintains a robust cyber program and can execute cyber attacks against the United States."

"Iran is capable, at a minimum, of carrying out attacks with temporary disruptive effects against critical infrastructure in the United States," it said.

Besides, the DHS warned that "homegrown violent extremists could capitalize on the heightened tensions to launch individual attacks," stressing that "an attack in the homeland may come with little or no warning."

Acting Secretary of Homeland Security Chad Wolf tweeted Saturday that his agency is actively monitoring and preparing for any specific and credible threat should one arise.

The US killing of Soleimani has sparked outrage in Iran, which has vowed to retaliate, as the international community is calling for utmost restraint from relevant sides to avoid a further escalation of tensions in the Gulf region.

Anti-war protests took place in many US cities, including Washington DC, New York, Chicago, Philadelphia and Los Angeles, on Saturday.

"For all who believe in peace, for all who are opposed to yet another catastrophic war, now is the time to take action," the Act Now to Stop War and End Racism coalition, which organized the events, said in a statement.