Despite its unmistakeable brutality and apparently lengthening arms to spread its campaign of terror, the Islamic State (ISIS) is not America's most dangerous enemy.

This is the view of New York Times bestselling author Robert Spencer, who is also the director of the online journal Jihad Watch.

In his latest book called "The Complete Infidel's Guide to Iran," Spencer says Iran, which has long branded the United States as the "Great Satan," actually poses the greatest threat not only to America but also to Israel and the West.

The reasons are many, and here are just some of them:

● Iran is the "terrorist powerhouse of the world." Spencer says the enemy has been made all the more dangerous by the "disastrous" nuclear deal with the United States and other powers "that barely restricts that nation's nuclear ambitions."

● The Iranian theocracy led by Supreme Leader Ali Khamenei has openly declared itself an enemy of the United States and also of anyone who dissents from its Shia brand of Islam.

● Iranian forces confront U.S. Navy ships in the Persian Gulf "on a near daily basis."

● Iran executes more of its citizens than any other nation in the world.

● Iran claims leadership of the global Islamic jihad which seeks nothing less than world conquest.

In the book, Spencer discloses that the United States and the other world powers actually surrendered to the mullahs in agreeing to a nuclear deal with Iran.

Spencer notes that the deal expires in 15 years, with no mechanism to keep Iran from continuing nuclear research and development, according to FrontPage Mag.

He cites other points in the agreement advantageous to Iran:

● Inspectors must give the mullahs up to 24 days' notice before entering suspect sites.

● Iran doesn't have to prove it's living up to the deal, since sanctions have already been removed, allowing Iran to get as much as $700 billion from renewed trade deals.

● There are no consequences for violating the terms of the deal.

Spencer also chronicles Iran's long-standing support for terrorists, including "shocking evidence" of its role in the 9/11 attacks on the United States.

He disputes Iran's claims that its nuclear weapons are only for deterrence or self-defence and explains why the Obama administration has grossly underestimated the Iranian threat to U.S. national security.

Spencer likewise outlines a new grand strategy on how Iran's Shi'ite terrorism might be contained and its threat to the United States reduced.

Iran already considers itself at war with America, Spencer points out. "If we refuse to recognise that fact, we are only falling prey to the mullahs' campaign of duplicity," he says.

As former Democratic Senator Joe Leiberman and U.N. Ambassador Mark D. Wallach reported last November, "Iran continues to act as a nuclear weapons outlaw."