The American airstrikes in northwestern Libya on Friday, which demolished an Islamic State training camp and were aimed at a top Tunisian operative, underscore the problem, Western officials said. The more than three dozen suspected Islamic State fighters killed in the bombing were recruited from Tunisia and other African countries, officials said, and were believed to be rehearsing an attack against Western targets.
Even as American intelligence agencies say the number of Islamic State fighters in Iraq and Syria has dropped to about 25,000 from a high of about 31,500, partly because of the United States-led air campaign there, the group’s ranks in Libya have roughly doubled in the same period, to about 6,500 fighters. More than a dozen American and allied officials spoke of their growing concern about the militant organization’s expanding reach from Libya and across Africa on rules of anonymity because the discussions involved intelligence and military planning.
Islamic State leaders in Syria are telling recruits traveling north from West African nations like Senegal and Chad, as well as others streaming up through Sudan in eastern Africa, not to press on to the Middle East. Instead, they are being told to stay put in Libya. American intelligence officials, who described the recent orders from Islamic State leaders, say the organization’s immediate goal is to carve out a new caliphate in Libya, and there are signs the affiliate is trying to establish statelike institutions there.
“Libya has become a magnet for individuals not only inside of Libya, but from the African continent as well as from outside,” John O. Brennan, the director of the C.I.A., told a Senate panel this month.
While administration officials have disclosed that Mr. Obama is mulling over how large of a military campaign to order for Libya, the new intelligence reports and the analysis on the spread of the Islamic State are energizing the high-level debate in Washington and allied capitals.
“The jihadist threat emanating from Syria and Iraq cannot be defused without addressing the growing danger posed by the terror groups’ co-conspirators in Libya,” Representative Devin Nunes, a California Republican who heads the House Intelligence Committee, said Friday.
New United States and allied intelligence assessments say that Islamic State commanders in Libya are seizing territory there, starting to tax its residents and setting up quasi-government institutions — mirroring the Islamic State playbook in Syria and Iraq.
“They’re trying to establish a statewide structure,” Brett McGurk, Mr. Obama’s envoy to the United States-led coalition fighting the Islamic State, told American lawmakers this month.
The militant group is also starting to move in on the lucrative African migrant-smuggling operations that have been thriving in lawless Libya, developing a new source of revenue for the terror group.
American officials caution that while the Islamic State’s Libya branch is trying to act like its parent organization in Syria, the affiliate faces some inherent limitations.
The Libya branch, unlike its Syria headquarters, does not control any oil fields that can generate revenue, although it has attacked some of the fields in eastern Libya.
The banks the franchise has seized in its stronghold of Surt were not as flush as the banks in Mosul — having around $500 million, by some accounts — when the Islamic State conquered that northern Iraqi city in 2014.
The Islamic State in Libya is swelling its ranks through one of the main means its parent in Syria uses: a savvy social media campaign aimed at enticing disaffected young people who are facing few education options and bleak economic futures in their countries.
Indeed, intelligence officials said there was emerging evidence that the Islamic State had turned to its affiliate in Nigeria — the Islamic militant organization called Boko Haram, which was formerly aligned with Al Qaeda — to poach young commanders and fighters from Al Qaeda’s affiliate in northwest Africa and from its Shabab franchise in Somalia.
Previous attempts by senior Islamic State leaders to reach out directly to those Qaeda groups received the silent treatment, the officials said. But the new approach, while still in its early stages, seems to be gaining traction.
The Senegalese authorities recently reported that 30 men had gone to Libya to fight with the Islamic State there, trends that officials in Niger, Nigeria and Mali have also noticed.
As the Islamic State pushes closer to some of the poorer countries of the Sahel region, like Niger and Mauritania, the authorities here believe there will be no shortage of unemployed young men who are eager to join the fight.
To help fight that trend, Special Forces from 30 African and Western countries are participating in a three-week counterterrorism training exercise here on this sprawling army encampment 35 miles outside Dakar that is also home to Senegal’s military academy.
On several shooting ranges, dotted with massive baobab trees, American, Canadian, Dutch and Belgian trainers worked with soldiers from Niger and Nigeria.
With help from Dutch Marines and American Special Forces, Senegal is also training a new force to patrol its watery northern border with Mauritania, and it is deploying troops to neighboring Mali to help a United Nations force stymie Qaeda and other militant fighters there.
“ISIS is spreading even to here,” said Col. Guirane Ndiaye, a Senegalese zone commander. “If we do not have a multinational effort, ISIS will spread even more.”