The Islamic State (ISIS) has at least 300 supporters in the United States—one-third of them women—and the number is rising as these supporters spread propaganda and hunt for other recruits, a new study from the George Washington University disclosed.

Researchers at the university's Program on Extremism said Twitter is the platform of choice of ISIS' U.S.-based sympathisers, NBC News reported.

What is remarkable is that even as Twitter management regularly suspends accounts that contain ISIS material, the accounts are immediately replaced with new ones to continue the spread of propaganda.

The George Washington University report said ISIS supporters even consider the taking down of their Twitter accounts as a "badge of honor."

The university researchers were able to monitor the recruitment of ISIS supporters in the U.S. for six months.

"In one case the seemingly naïve individual posted general questions about religion, to which ISIS supporters quickly responded in a calm and authoritative manner," the authors wrote.

"After a few weeks, the accounts of hardened ISIS supporters slowly introduced increasingly ardent views into the conversation. The new recruit was then invited to continue the conversion privately, often via Twitter's Direct Message feature or on other private messaging platforms such as surespot."

The report was also able to find out how U.S. jihadists meet and recruit in person, revealing clusters of ISIS supporters meeting in various cities.

"One of them, located in Texas, revolves around a few charismatic individuals and an Islamic studies group. Another, based in the suburbs of a large Midwestern city, appears to be composed of former high school friends and a handful of their acquaintances," the report said.

Seamus Hughes, deputy director of the university's Program on Extremism, noted that while American ISIS sympathisers are mostly male, nearly a third of the accounts they examined appeared to be used by women.

"They communicate primarily in English, and discuss a wide range of topics, from open support of terrorist attacks to boringly benign banter about everyday life," he said. "The online scene is a bit of a close-knit clique, where inside jokes are shared, memes are created, and dissenters are quickly ignored."

J.M. Berger, a social media counterterrorism analyst and co-author of a book about ISIS, said the report's analysis of offline clusters was highly revealing.

"For all that we talk about social media, there is still a significant role for face to face interaction," he said.