The group that launched the Sept. 11 attacks, waged insurgent war against U.S. forces in Afghanistan, catalyzed extremist movements in places like Iraq, Yemen, Somalia and North Africa, and was supposed to have been all but "decimated" and hiding in Pakistan's tribal regions has found new life in the conflict in Syria, and according to the Defense Department is on the rise there.

The U.S. conducted an airstrike in Syria on Monday morning against an operative in what Pentagon spokesman Navy Capt. Jeff Davis described as "core al-Qaida." Davis wouldn't confirm the effect of the strike or even the target itself, though local media reported it was Abu Farag al-Masri, an Egyptian and senior commander of an al-Qaida affiliate.

The strike was against a "prominent al-Qaida leader," Davis said, adding that the military has observed "a bit of a growth of core al-Qaida in Syria."

The revelation indicates increased danger for the U.S. from Syria, a veritable cauldron of violence that now serves as one of the most likely havens from which terrorist groups can plan and execute attacks abroad.

"Al-Qaida central is not decimated. I'd put it as simply as that," says Charles Lister, a terrorism expert and senior fellow at the Middle East Institute. "If anything, they are rapidly revitalizing themselves on Syrian territory, which should be of serious concern."

President Barack Obama and other top U.S. government officials refer to "core al-Qaida" or "al-Qaida central" in the context of having been decimated by U.S. military and intelligence operations during the war in Afghanistan. According to the Pentagon, it differs clearly from other extremist networks operating internationally and on the ground in Syria, such as the Islamic State group, which formally separated itself from al-Qaida after its public rise in 2011; the Khorasan group, considered the experimental arm of al-Qaida's planning operations; or the Nusra Front, now known as Jabhat Fateh al-Sham, a Syrian al-Qaida affiliate that has operated in close tandem with elements of the Syrian opposition fighting the regime of Bashar Assad, including reportedly some opposition groups the U.S. has supported.

The al-Qaida that Osama bin Laden founded, now under the leadership of the elusive Ayman al-Zawahiri, sees Syria as an opportunity to establish a second and much more central base of operations where it would have greater access to its enemies. Since 2012, Western intelligence has tracked its operatives moving in and out of Syria from places like Iran, Yemen, Central Asia and elsewhere in the Middle East.

"There's been a movement over the last three to four years by al-Qaida in Afghanistan and Pakistan to throw as much resources as possible into Syria because of what it represents: the potential opportunity to have an Afghanistan of the late 1990s but this time in Syria, practically on Europe's doorstep with easy access to Turkey and then back into Syria," Lister says.

Further complicating the danger in Syria are U.S. attempts to defeat Islamic extremist groups while staying uninvolved in the civil war between opposition fighters and the Assad regime. Experts now fear America cannot differentiate clearly between the myriad terrorist groups operating there, particularly following reports that elements of the Syrian opposition movement it helps to train and equip subsequently turned to organizations like the Nusra Front for on-the-ground assistance.

"On the one hand, we're targeting senior members in Jabhat Fateh al-Sham who are legacy al-Qaida members and current al-Qaida figures. And by the same token, we have supported groups that fight alongside them as allies. It doesn't make any sense," says Thomas Joscelyn, a senior fellow at the Foundation for the Defense of Democracies who tracks al-Qaida movements for its publication, The Long War Journal.