President Donald Trump seriously considered attacking an Iranian nuclear facility in a pre-emptive strike last week, but dropped the idea after a White House meeting with top aides.

However, the plan to strike Iran has not been dropped completely, if the latest reports can be believed. A Washington Post story says that Trump has laid out a 'Tripwire' for Iran -- if any American is killed in an action that can be tied back to Iranian hands, a retaliation will be swift and certain.

Trump would not shy away from using a trigger to launch a full-scale strike on Iran, sources cited by the Post suggest. The revelation follows a report by The New York Times that said Trump mulled attacking an Iranian nuclear facility last week.

Iran nuclear programme
ran Nuclear Deal Talks: US Secretary of State John Kerry (L), US Secretary of Energy Ernest Moniz (2L), Robert Malley (3L), of the US National Security Council, European Union High Representative Federica Mogherini (C), Head of Iranian Atomic Energy Organisation Ali Akbar Salehi (2R) Reuters

Only a Pre-emptive Strike is Off the Table

The question whether to attack Iran was popped during an Oval Office meeting which was attended by Vice President Mike Pence, Secretary of State Mike Pompeo, acting Defense Secretary Christopher Miller and General Mark Milley, chairman of the Joint Chiefs of Staff.

The official who leaked the information to the New York Times said top national security advisers apprised Trump of the consequences of such an attack. They warned that an attack on Iran at this point might trigger a broader conflict. "He asked for options. They gave him the scenarios and he ultimately decided not to go forward," the official said.

Now it seems that what's off the table is a pre-emptive strike on Iran. The Trump administration, which is in its final weeks, will nonetheless go ahead with an attack on Iran in the event of an attack in the region that can be linked to Iran. The scenario raises the possibility of the US launching a strike on Iran before January 20th, the report says.

Iran missile test
A ballistic missile is launched and tested in an undisclosed location, Iran Reuters

Attack on Baghdad's Green Zone

The Post story cites Tuesday's attack on Baghdad's Green Zone for the context. The attack, launched possibly by an Iranian-backed Iraqi militia, killed a child and injured five civilians. There were no American casualties. The target was the US embassy in the Green Zone, but the four Katyusha rockets fell outside the heavily fortified target area, Iraqi officials said.

The report says that the thinking inside the Trump administration is that if similar attacks kills an American, Trump could order a retaliatory strike on Iran.

Trump toyed with the idea of taking down Iran's nuclear research facilities a day after the International Atomic Energy Agency (IAEA) said Tehran is steadily increasing its stockpile of low-enriched uranium. The IAEA also said in its latest report that Iran now has a stockpile of 2,442.9 kilograms of low-enriched uranium, up from 2,105.4 kilograms reported on August 25.