The Islamic State of Iraq and Syria has launched a blood-curdling Twitter campaign using the hashtag #CalamityWillBefallUS to threaten U.S. citizens and interests around the world if it intervenes to prevent their march through northern Iraq.

The "Warning To American People" campaign urges supporters to tweet the anti-American hashtag along with photos warning the U.S. against attacking the extremist group in Iraq.

ISIS supporters have tweeted the hashtag hundreds of times with harrowing threats of attacks on the U.S., alluding to 9/11, and pictures of U.S. troops killed and maimed in both Iraq and Afghanistan with some users asking: "Do you want more?" 

One user tweeted: "Any company in Arab countries which employs Americans is a legitimate target for every Muslim."

Among many tweets mentioning 9/11, one user wrote: "#11sep was from your hand & you'll get more by attacking us...just try not to...for your safety."

Another tweeted: "Our convoys will destroy your fake civilisation as soon as we step on your land!"

As the group has advanced through Iraqi's north and west, capturing the cities of Mosul and Tikrit, their electronic efforts have redoubled via their social media outlets and al-Hayat media, wing with a number of high-quality videos emerging.

The Islamist group's campaign of propaganda has included a newly released video titled, "There is No Life Without Jihad" where five of the group's mujahideen, from Australia and the United Kingdom, pledge to take their holy war to Jordan and Lebanon.

Along with its Islamic State Report publication and the recruitment videos, ISIS has used a Twitter app named "dawn of glad tidings" to boost the numbers of messages it is able to send out to its followers.

ISIA has launched its online propaganda operation in the hope of recruiting new members in the fight to create an Islamic caliphate straddling the now-erased Syria-Iraq border.

The "Warning To American People" guide emphasizes that "tweeting in English is preferred" during the campaign, signaling that the group hopes to lure Western jihadis to the cause. 

This aim has been spelled out in the 13-minute video "There is No Life Without Jihad" where five of the group's mujahideen, from Australia and the United Kingdom, issue an impassioned recruitment message to those in their home countries.

A mixture of foreign fighters have flocked to the region to fight for ISIS, with mujahideen from Bangladesh, Iraq, Cambodia, Australia, United Kingdom and Chechnya confirmed as having joined the group.

The propaganda barrage reportedly eased the capture of Mosul, Iraq's second city, as Iraqi security forces fled their positions through fear rather than force.

With the appearance of the group's black flag in Mosul, the soldiers feared that they would face a gruesome death if they were captured by the group after reports of their barbaric killings.

While ISIS has cemented its position as the top global jihadi brand on the Internet, other groups continue to vie for influence.

Jabhat al-Nusra, ISIS' rival in Syria, which is more directly tied to al Qaeda, has a network of tweeters who attempt to spread the group's message while al Qaeda offshoots in Egypt and Yemen regularly post videos of their actions.