What Is the Khorasan Group, Targeted By US in Syria? Al Qaeda group purportedly was "nearing execution phase" for attack.

 -- [This story has been updated, 9/24.]

The U.S. military said today that by striking a little known terror cell called the Khorasan Group in Syria it was able to take out dangerous men who were “plotting and planning imminent attacks against Western targets to include the U.S. homeland.”

In the midst of the well-publicized campaign against the Islamic State of Iraq and Syria (ISIS), the military’s first official announcement that a different, potentially more deadly terror group existed, that it’s members were planning an “imminent” attack on America and that those planning the attack had been killed in the U.S.-led bombing campaign all came as something of a surprise, considering that for the public, the group was virtually unheard of until a few days ago.

So here’s what we know so far about the mysterious Khorasan Group:

What Is the Khorasan Group?

The Khorasan Group is a relatively small al Qaeda unit – made up of just some 50 hardened fighters with mixing jihadist affiliations, according to a half-dozen officials with knowledge of the group. As the U.S. military’s Central Command put it, they are “seasoned al Qaeda veterans.” A senior administration official told reporters the group grew out of al Qaeda's old core group in Afghanistan.

"It's the same cast of characters we have had our eye on for some time," the official said.

Back in June, ABC News reported that an alliance had been building inside Syria between al Qaeda operatives there and those from al Qaeda’s dangerous Yemen-based branch, al Qaeda in the Arabian Peninsula (AQAP), home to expert bomb makers. Sources told ABC News today some of those allied jihadis, then unidentified, made up the Khorasan Group.

The group is not thought to be affiliated with ISIS, which had a public falling out with al Qaeda earlier this year. In fact, the Khorasan Group’s leader may have been tasked with fighting ISIS in Syria as well as the West, according to government documents and reports in the Long War Journal, as part of the larger, violent conflict between ISIS and al Qaeda’s Syrian affiliate, al-Nusra Front.

Digital Feature: What Is ISIS?

The word Khorasan denotes greater Afghanistan, parts of central Asia and China’s Xinxiang province. The term has religious significance in the context of jihad and several organizations in the region use the name in various ways.

Who Is Muhsin al-Fadhli?

Muhsin al-Fadhli, initially described in reports as the Khorasan Group’s leader, is the only member to be publicly identified. An intelligence official told ABC News that the Khorasan Group has no official leader.

While there’s scant information about the organization to which he belongs, al-Fadhli has a long international rap sheet.

He’s wanted in the U.S. for his work as an “Iran-based senior al Qaeda facilitator and financier,” according to the State Department, and is suspected of being one of Osama bin Laden’s most trusted operatives – one of the few aware of the 9/11 attacks before they happened.

Al-Fadhli, 33, was designated a terrorist by the U.S. back in 2005 for providing “financial and material support to the al-Zarqawi Network and al Qaeda,” the State Department said. Ironically over the years the al-Zarqawi Network in Iraq would mutate into what is now ISIS.

“…[P]rior to that [al-Fadhli] was involved in several terrorist attacks that took place October 2002, including the attacks on the French ship MV Limburg and against U.S. Marines on Faylaka Island in Kuwait,” the U.S. Treasury said.

The United Nations added al-Fadhli to its al Qaeda Sanctions Committee list in 2005 as well. The same year, President Bush mentioned al-Fadhli, then just 23, by name in a speech, saying that the U.S., working with others, would “bring him to justice.”

The State Department offers a $7 million reward for information leading to his capture. While the U.S. military said Khorasan Group individuals were killed in the recent strikes, they did not identify any specifically.

So If They’re a Big Deal, Why Haven’t I Heard of Them?

Unlike previous terrorist foes, the U.S. government apparently worked to keep a tight lid on the identity of the Khorasan Group despite, as a senior administration official put it, the government watching the threat from the group “for some time.”

Though ABC News reported an air travel scare this summer that sources said today were linked to the group, the name “Khorasan Group” wasn’t used in the Western media until earlier this month when The Associated Press first identified them. Even after that, when Rep. Peter King, R-N.Y., brought up the name in an open Congressional hearing last week, Department of Homeland Security Jeh Johnson paused awkwardly before telling King that “discussion of specific organizations, I think, should be left to a classified setting.”

Director of National Intelligence James Clapper, however, used the name a day later in a briefing with reporters, and profiles of the group followed in some major newspapers.

Still, today was the first time U.S. officials spoke so openly about the group, and it was the first time President Obama used the term in a public setting.

What Does The Khorasan Group Want With the U.S.?

Unlike ISIS, which is attempting to establish an Islamic kingdom centered in Syria and Iraq through large land grabs and local governance, U.S. officials say that as an al Qaeda group, Khorasan’s goal is to attack the West in spectacular fashion – and that such plots appear to be “imminent.”

“We had very good indications that this group, which is a very dangerous group, was plotting and planning imminent attacks against Western target to include the U.S. homeland,” Kirby told ABC News’ “Good Morning America”. “We knew that there was active plotting going on for an attack on the U.S. homeland.”

Later, Lt. Gen. William Mayville told reporters the U.S. believed Khorasan Group to be “nearing the execution phase” for an attack in Europe or the American homeland, likely using Western recruits to execute the plot.

A senior administration official told reporters the Obama administration had "been watching this threat from the Khorasan Group for some time and had contemplated action separate and apart from the growing threat from ISIL [ISIS]," but seized the "opportunity" to strike them at the same time as ISIS Monday night.

AQAP, the terror group’s Yemen affiliate from which some Khorasan fighters are said to come and home to al Qaeda’s master bomb maker Ibrahim al-Asiri, has managed multiple times to get explosives on board U.S.-bound aircraft, but each either failed to explode or was intercepted before its final destination. In one case, a refined version of an underwear bomb was smuggled out of the terror group’s control by an insider who was actually working for allied spy agencies.

In ABC News’ June report, sources said groups inside Syria, now believed to include the Khorasan Group, were working to produce new and “creative” designs for explosives that could evade airport security. In July the Department of Homeland Security increased security at airports and announced that “powerless” electronic devices would not be allowed on board a plane. Senior law enforcement and intelligence officials told ABC News today the Khorasan Group was the cause of the heightened security.

But After the Airstrikes, Are They Still a Threat?

Kirby said that the military believes that “the individuals that were plotting and planning it have been eliminated” but said the military is going to “continue… to assess the effectiveness of our strikes going through today.”

Security sources told ABC News they feared Kirby’s statement was too certain and said that the group was more likely just degraded in the strikes.

When asked if there was a continuing threat to the U.S., Mayville asked that the military be given “some time to assess” the strikes.

In an address to the nation today, President Obama said of the strikes on Khorasan that “once again it must be clear to anyone who would plot against America and try to do Americans harm that we will not tolerate safe havens for terrorists who threaten our people.”

CLICK HERE to return to the ABC News Investigative Unit homepage.