The report said the move came after a mortar attack launched by an Iran-linked group on the Baghdad diplomatic quarters home to the US embassy in September. No one was hurt by the shells, which landed in an open lot.

But the White House National Security Council (NSC) sought to develop a forceful American response to the low-scale attack, including options for a strike against the Islamic republic, the Journal reported.

It added that the NSC also requested options to respond with strikes in Iraq and Syria.

"It definitely rattled people," a former senior US administration official told the newspaper. "People were shocked. It was mind-boggling how cavalier they were about hitting Iran."

Although the Defense Department did develop proposals for a possible strike, the Journal said it was unclear whether they were shared with the White House.

In one NSC meeting, then deputy national security advisor Mira Ricardel called the attacks in Iraq an "act of war" and called for a decisive US response.

Pentagon officials stressed that it was not unusual for the Defense Department to draw up military plans for the White House.

"The Department of Defense is a planning organization and provides the president military options for a variety of threats," Colonel Rob Manning, a Pentagon spokesman, told AFP.

He said the Pentagon's activities include "routinely reviewing and updating plans and activities to deal with a host of threats, including those posed by Iran, to deter and, if necessary, to respond to aggression."

Asked about the report during his Middle East trip, US Secretary of State Mike Pompeo declined comment.

After the attack in Baghdad, the White House warned that "the United States will hold the regime in Tehran accountable for any attack that results in injury to our personnel or damage to United States government facilities."

"America will respond swiftly and decisively in defense of American lives," it added.

National Security Advisor John Bolton, a known Iran hawk, has pressed for regime change in the Islamic republic.

He penned a 2015 New York Times opinion piece prior to his current role titled "To stop Iran's bomb, bomb Iran."