SHAFAQNA (International Shia News Association) As the United States begins what could be a lengthy military campaign against the Islamic State, intelligence and law enforcement officials said another Syrian group, led by a shadowy figure who was once among Osama bin Laden’s inner circle, posed a more direct threat to America and Europe.
American officials said that the group called Khorasan had emerged in the past year as the cell in Syria that may be the most intent on hitting the United States or its installations overseas with a terror attack. The officials said that the group is led by Muhsin al-Fadhli, a senior Qaeda operative who, according to the State Department, was so close to Bin Laden that he was among a small group of people who knew about the Sept. 11, 2001, attacks before they were launched.
There is almost no public information about the Khorasan group, which was described by several intelligence, law enforcement and military officials as being made up of Qaeda operatives from across the Middle East, South Asia and North Africa. Members of the cell are said to be particularly interested in devising terror plots using concealed explosives. It is unclear who, besides Mr. Fadhli, is part of the Khorasan group.
The director of national intelligence, James R. Clapper Jr., said on Thursday that “in terms of threat to the homeland, Khorasan may pose as much of a danger as the Islamic State.”
Some American officials and national security experts said the intense focus on the Islamic State had distorted the picture of the terrorism threat that has emerged from the chaos of Syria’s civil war, and that the more immediate threats still come from traditional terror groups like Khorasan and the Nusra Front, which is Al Qaeda’s designated affiliate in Syria.
Mr. Fadhli, 33, has been tracked by American intelligence agencies for at least a decade. According to the State Department, before Mr. Fadhli arrived in Syria, he had been living in Iran as part of a small group of Qaeda operatives who had fled to the country from Afghanistan after the Sept. 11 attacks. Iran’s government said the group was living under house arrest, but the exact circumstances of the Qaeda operatives were disputed for years, and many members of the group ultimately left Iran for Pakistan, Syria and other countries.
In 2012, the State Department identified Mr. Fadhli as Al Qaeda’s leader in Iran, directing “the movement of funds and operatives” through the country. A $7 million reward was offered for information leading to his capture. The same State Department release said he was working with wealthy “jihadist donors” in Kuwait, his native country, to raise money for Qaeda-allied rebels in Syria.
In a speech in Brussels in 2005, President George W. Bush referred to Mr. Fadhli as he thanked European countries for their counterterrorism assistance, noting that Mr. Fadhli had assisted terrorists who bombed a French oil tanker in 2002 off the coast of Yemen. That attack killed one and spilled 50,000 barrels of oil that stretched across 45 miles of coastline.
The Islamic State, also known as ISIS or ISIL, is viewed as more focused on consolidating territory it has amassed in Syria and Iraq than on attacking the West. Some even caution that military strikes against the Islamic State could antagonize that group into planning attacks on Western targets, and even benefit other militant organizations if more moderate factions of the rebellion are not ready to take power on the ground.
The Islamic State’s recent statements, including a video using a British captive as a spokesman, have sought to deter American action against the group and threatened attacks only as revenge for American strikes.
At the same time, the rise of the Islamic State has blunted the momentum of its rival groups in Syria, including the Nusra Front, once considered to be among the most capable in the array of Syrian rebel groups. The Islamic State’s expansion across northern Iraq and in oil-rich regions of eastern Syria has sapped some of the Nusra Front’s resources and siphoned some of its fighters — who are drawn by the Islamic State’s battlefield successes and declaration of a caliphate, the longtime dream of many jihadists.
It is difficult to assess the seriousness and scope of any terror plots that Khorasan, the Nusra Front or other groups in Syria might be planning. In several instances in the past year, Nusra and the Islamic State have used Americans who have joined their ranks to carry out attacks inside Syria — including at least one suicide bombing — rather than returning them to the United States to strike there.
Beyond the militant groups fighting for control of territory, Syria has become a magnet for Islamic extremists from other nations who have used parts of the country as a sanctuary to plot attacks.
“What you have is a growing body of extremists from around the world who are coming in and taking advantage of the ungoverned areas and creating informal ad hoc groups that are not directly aligned with ISIS or Nusra,” a former senior law enforcement official said.
Spokesmen for the C.I.A. and the White House declined to comment for this article.
The grinding war in Syria, well into its fourth year, has led to a constant shifting of alliances among the hard-line rebel groups.
Ayman al-Zawahri, the head of Al Qaeda, anointed the Nusra Front as its official branch in Syria and cut ties with the Islamic State early this year after it refused to follow his orders to fight only in Iraq. Officials said that Khorasan was an offshoot of the Nusra Front. According to a new report by the Bipartisan Policy Center, a nonprofit research and analysis organization, the rifts among these various groups “threaten to create a conflict throughout the jihadist movement that is no longer confined to Syria and Iraq.”
While Nusra has been weakened, it remains one of the few rebel organizations that has active branches throughout Syria. Analysts view the organization as well placed to benefit from American strikes that might weaken the Islamic State.
Jennifer Cafarella, a Syria analyst with the Institute for the Study of War in Washington, said that American strikes could benefit the Nusra Front if the United States did not ensure that there was another force ready to take power on the ground.
“There is definitely a threat that, if not conducted as a component of a properly tailored strategy within Syria, the American strikes would allow the Nusra Front to fill a vacuum in eastern Syria,” she said.
She noted that the Nusra Front had been the primary force in the eastern province of Deir al-Zour before it was pushed out by the Islamic State earlier this year, and that the group had maintained better relationships with the local tribes than ISIS had. This could make it easier for the group to return if ISIS is chased out by American airstrikes.
While the Nusra Front does not openly call for attacks on the West, it remains loyal to Mr. Zawahri, whose clout among jihadists has waned with the rise of the Islamic State.
A great deal remains uncertain about the Nusra Front’s ultimate aims inside Syria. Hamza al-Shimali, the head of the American-backed rebel group the Hazm Movement, said that he and his allies did not trust the Nusra Front. He said he feared that one day he would have to fight the Nusra Front in addition to the Syrian government and the Islamic State.
American intelligence officials estimate that since the Syrian conflict began, about 15,000 foreigners, including more than 100 Americans and 2,000 Europeans, have traveled to the country to fight alongside rebel groups. Syria’s porous borders make it relatively easy to get in and out of the country, raising concerns among Western officials that without markings on their passports they could slip back undetected into Europe or the United States.