WASHINGTON—The threat to the U.S. from global jihadist groups has escalated in the past three years, with the number of groups increasing by more than 50% and the estimated number of militants doubling, according to a report to be released on Thursday.
The report by the Rand Corp. think tank, which used public data to take a kind of global census of al Qaeda and related groups, will say the civil war in Syria has been the largest driver of the growth of jihadist activity. Syria is the location that has seen the greatest growth in number of groups and numbers of militants, which now make up more than half of the number of al Qaeda-sympathizing jihadists world-wide.
"It's become a breeding ground for jihadist activity," said the report's author, Seth Jones, associate director of Rand's International Security and Defense Policy Center.
In the past few months, militants there have shown growing interest in tapping Western resources and mounting attacks outside Syria, he said, noting last week's suicide attack by an American in Syria, in addition to recent arrests of alleged Syrian-trained fighters in France and Spain, as well as one allegedly involved in a deadly shooting last month in Belgium.
The Rand findings also cast doubt on the Obama administration's efforts to end the U.S. military presence in Afghanistan by 2016 and keep Syria at arm's length. A complete withdrawal from Afghanistan, the report said, "could seriously jeopardize U.S. security interests," because of the continuing terrorist presence in Afghanistan and Pakistan. It also calls for a "more aggressive strategy" in Syria, either clandestinely or working with locals.
National Security Council spokeswoman Caitlin Hayden said she couldn't comment on a report that hadn't been released, but referred to President Barack Obama's speech last week where he announced ramped-up partnerships with local allies. In that speech, Mr. Obama also said "U.S. military action cannot be the only—or even primary—component of our leadership in every instance."
The report, prepared for the defense secretary, appears to be the first public census of al Qaeda and related terrorism groups. It focuses exclusively on "Salafi jihadists," which subscribe to al Qaeda's brand of violent jihad.
The number of al Qaeda-sympathizing jihadist groups jumped to 49 from 31 between 2010 and 2013. The number of jihadists has surged similarly. Because it is difficult to get a precise count of jihadist group membership, the report provides ranges. It estimates the total number grew to between 45,510 and 105,510 in 2013, from between 12,945 and 47,810 in 2010.
The biggest increase during that period came in Syria. But there were ample increases in North Africa as well, particularly in Libya.
Egypt is the one key country that has posted a decline since the government's recent crackdown on terrorism, including the arrest last year of the leader of an aspiring al Qaeda affiliate there, Muhammad Jamal Abu Ahmad.
The report categorizes groups by the threat level they pose to the U.S. Those posing a high threat are engaged in active plotting against the U.S. homeland and targets overseas, such as al Qaeda's affiliate in Yemen and its core leadership in Pakistan, as well as some other individuals and networks. Those posing a medium threat with active plotting against U.S. interests overseas include al-Shabaab in Somalia, Ansar al-Shaira in Libya, al Qaeda's North African affiliate, and the Muhammad Jamal Network.
The report found that at the moment, though, al Qaeda and its affiliates are largely focused on attacking "near" local enemies instead of "far" Western ones, with 99% of the al Qaeda-related attacks in 2013 targeting "near enemies" in North Africa and the Middle East.
The report supports broad findings by U.S. intelligence agencies that al Qaeda and its affiliates are increasingly decentralized, and the report paints a picture of a diverse set of groups that often disagree on key issues such as the advisability of allowing civilian casualties and whether to attack abroad or within their countries or regions.