"It comes as the U.K. closed its embassy in Tehran while other European countries urge residents to flee. Tehran has also closed its airspace to all flights, except those with previous permission from the Iranian Civil Aviation Organisation.

"President Trump is ready to push the button on Iran," the source said. "It will be a surgical removal of the regime."

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"The one thing that the president is waiting on is that the Iranian banks are on the point of collapse which means the IRGC [Islamic Revolutionary Guard Corps] and others will not get paid once that happens," they added.

"If that happens, then the regime will collapse by itself and the president is waiting on that " but he will not wait long."

It comes as the U.S. withdrew personnel from its Al-Udeid air base in Qatar on Wednesday, the Middle East's largest U.S. base housing around 10,000 troops. One official told Reuters the decision was a precaution given heightened regional tensions."