The Islamic State has recruited thousands of supporters in the United States, far more than previously thought, according to a scathing new report, raising the likelihood that supporters of the terrorist army could be plotting attacks similar to those carried out in Paris.

And the "challenges of screening incoming refugees" from Muslim countries may be adding fuel to the fire, according to the report, authored by national security experts at the Threat Knowledge Group.

The report accuses Obama of "downplaying" the threat of ISIS while adding to the threat by importing Muslim refugees that are difficult to screen.

The U.S. has imported 70,000 refugees per year for many years, more than half of them from Muslim-dominated countries such as Somalia and Iraq with active jihadist movements, and President Obama has pledged to increase that number to 85,000 this year and 100,000 the following year.

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The new study is significant because the Obama administration has in the past made statements that "around 200" Americans had left the country to join ISIS and could come back at any time using their American passports.

The FBI has said it has about 900 active ISIS investigations in all 50 states but never given an estimate of how big the contingent of ISIS sympathizers may be in the U.S.

The Threat Knowledge Group's chairman is counter-terrorism expert Sebastian Gorka, a Department of Defense adviser. The group, which includes academics and policy advisers, has put together a list of 82 persons in the United States who were affiliated with the Islamic State, also known as ISIS, and apprehended by law enforcement officials, including those who traveled or attempted to travel to Iraq and Syria, launched domestic attacks, or participated in recruiting or fundraising.

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The 20-page report says that almost one third of these individuals had plotted attacks against Americans on U.S. soil in the last 18 months.

Through ISIS propagandists using social media, the Islamic terrorist group has been able to attract hundreds more supporters in the United States.

"Based on the evidence available, the number of ISIS supporters in the United States measures in the thousands, rather than hundreds," Gorka said in the report, whivh he co-authored with his wife, Katharine Gorka.

At the end of the report, the Gorkas give five recommendations on how to counter the threat.

Atop the list is a warning given in no uncertain terms: "Stop downplaying the seriousness of the threat so that individuals and law enforcement can be properly prepared."

Whether ISIS will indeed launch an attack on the scale of the Paris attack – which killed 130 people and injured 350, is unknown, the report says.

"But it is clear that the United States is a primary target for ISIS and that ISIS has the necessary supporters in place and the financial means to carry out such an attack. The challenges of screening incoming refugees may further exacerbate the problem. "While accepting those who flee from persecution and violence is a valued component of the American tradition, we must acknowledge that ISIS and other terrorist groups may use the refugee track as a way to gain access to the United States with the purpose of carrying out an attack."

After examining arrests of ISIS terrorists on a per-month basis, the Gorkas found that U.S. police are interdicting 300 percent more Islamic State recruits than al-Qaida supporters.

The Islamic State has been able to attract thousands of foreign fighters and U.S. supporters through its aggressive dissemination of propaganda on social media and urgent ideological and religious narrative.

Ali Shukri Amin, a 17-year-old Virginia resident and Islamic State supporter who was sentenced to 11 years in prison in August, used his Twitter account with 4,000 followers to raise funds for the group and encourage friends to join it overseas, the Washington Free Beacon reported.

Ahmad Musa Jibril, an imam in Dearborn, Michigan, who has also spent time in jail for money laundering and tax evasion, also points to the terrorist group’s online reach. Jibril has more than 38,000 Twitter followers, though he has not tweeted since last July and may have found other methods of communication, according to the Free Beacon. He is reported to have a large following among foreign fighters in Iraq and Syria.

Religious authorities for the group claim that the "end times" are now coming to pass when Muslims will defeat invading Christians in Syria in “the final jihad” before the world ends and devout Muslims ascend to heaven.

"They are able to persuade many supporters to come fight on the grounds that this is 'The Final Jihad,'" the Gorkas said.

The Islamic State also focuses on young recruits. The report notes that 63 percent of those arrested in the United States for supporting the group were between the ages of 15 and 25.

Islamic State supporters often recruit in clusters around the United States, with friends and family members forming a local jihad network.

"For law enforcement, it suggests that if one person in a community affiliates themselves with ISIS, one can expect to see more, especially among those who are close to the recruit," the Gorkas said.

But Islamic State adherents in the United States are prone to capture.

Among the 82 cases of U.S. supporters studied by the Threat Knowledge Group, about 60 percent were identified by authorities through their social media posts or a tip from a friend or family member. The Gorkas recommended police build trust in communities so families and residents will feel comfortable turning in those they suspect have become jihadists.

They also urged police to work with educators to identify the signs of radicalization among students, focus more on tracking the Islamic State's religious propaganda online, and develop a more rigorous screening process for refugees from the Middle East.