Supporters of Islamic State could control as many as 90,000 Twitter accounts worldwide, a new study suggests.
The terror group exerts "an outsized impact on how the world perceives it" through social media and its online following, according to the Washington-based Brookings Institute report.
It recommends that governments and social media companies find new ways of tackling Islamist accounts, which have been used to post gruesome propaganda content.
The report, by Brookings academic JM Berger and technologist Jonathon Morgan, says: "While we do not believe that any mainstream social media platform wishes to see its services used to further acts of horrific violence, we also suspect some would rather not be bothered with the challenge of crafting a broad and coherent response to the issue.
"While we can sympathise with the challenges and dilemmas such a response would entail, it is clear that social media companies do feel an obligation to respond to some social standards and illegal uses of their services.
"We are not aware of any major company that takes a hands-off approach to the use of its platform to promote child pornography or human trafficking - or, less dramatically, phishing, spam, fraud, and copyright violations.
"Extremism, while raising thornier issues, merits attention, especially when faced with a rising challenge of violent groups who manipulate platforms to reap the rewards of spreading images of their cruelty."
Twitter has been used, alongside other platforms, to spread gruesome images of murders carried out by IS, including of Western hostages. It has also been linked to radicalisation.
Last month it was revealed that Shamima Begum, 15, one of three London schoolgirls who are believed to have run away to join IS previously sent a tweet to Aqsa Mahmood, who left Glasgow for Syria to be a "jihadi bride" in 2013.
Aqsa Mahmood, left, and Shamima Begum
Privately-educated Ms Mahmood is reported to have encouraged terrorist acts via a Twitter account under the name Umm Layth.
Her family branded her a "disgrace" and expressed anger that she may have tried to recruit Shamima and her friends Kadiza Sultana, 16, and 15-year-old Amira Abase, all from Bethnal Green.
Their disappearance prompted Prime Minister David Cameron to say that internet companies must live up to their "social responsibility" by taking down extremist content and improving co-operation with the authorities over contacts between extremists and young people vulnerable to radicalisation.
Islamic State militants recently threatened to kill Twitter boss Jack Dorsey over the blocking of their accounts
The study of IS-linked accounts between September and December estimated there were between 46,000 and 70,000, with the researchers believing that the true figure was towards the lower end of this scale but setting an absolute maximum at 90,000.
Their analysis was based on "robust" data collected about 50,000 accounts, and partial information about a further 1.9 million.
Only a tiny fraction of accounts revealed locations, of which the vast majority were in the Middle East and North Africa. Single figure numbers were found in the UK, France, Spain, Italy, Switzerland, Belgium and Australia.
The report noted that platforms including Facebook and YouTube have already introduced changes aimed at tackling extremism.
Twitter had started suspending accounts linked to IS - also known as Isis - by the time the research was started, but the authors said this created a new risk, arguing: "While suspensions appear to have created obstacles to supporters joining Isis's social network, they also isolate Isis supporters online.
"This could increase the speed and intensity of radicalisation for those who do manage to enter the network, and hinder organic social pressures that could lead to de-radicalisation.
"Further study is required to evaluate the unintended consequences of suspension campaigns and their attendant trade-offs. Fundamentally, tampering with social networks is a form of social engineering, and acknowledging this fact raises many new, difficult questions."
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