The US says it has hit a little-known group called "Khorasan" in Syria, but experts and activists argue it actually struck Al-Qaeda's affiliate Al-Nusra Front, which fights alongside Syrian rebels.
In announcing its raids in the northern province of Aleppo on Tuesday, Washington described the group it targeted as Khorasan, a cell of Al-Qaeda veterans planning attacks against the West.
But experts and activists cast doubt on the distinction between Khorasan and Al-Nusra Front, which is Al-Qaeda's Syrian branch.
"In Syria, no one had ever heard talk of Khorasan until the US media brought it up," said Rami Abdel Rahman, director of the Britain-based Syrian Observatory for Human Rights.
"Rebels, activists and the whole world knows that these positions (hit Tuesday) were Al-Nusra positions, and the fighters killed were Al-Nusra fighters," added Abdel Rahman, who has tracked the Syrian conflict since it erupted in 2011.
Experts were similarly dubious about the distinction.
"The name refers to Al-Qaeda fighters previously based in Afghanistan, Pakistan, and Iran who have travelled to Syria to fight with... Al-Nusra," said Matthew Henman, head of IHS Jane's Terrorism and Insurgency Centre.
"They... should not be considered a new or distinct group as such."
Aron Lund, editor of the Syria in Crisis website run by the Carnegie Endowment for International Peace, raised similar doubts.
"The fact that news about this Al-Qaeda-run, anti-Western cell linked to Al-Nusra emerged just over a week ago, through US intelligence leaks -- well, it's certainly an interesting coincidence," he told AFP.
"And it certainly helped make the case for attacking them, for why this mattered to US national security, and for why this was not about attacking a rebel group in Syria but about attacking a group hostile to the US."
- Rebels allied with Nusra -
Claims of a distinction are lost of many of Syria's rebels, who have also often rejected the world community's designation of Al-Nusra as a "terrorist" group.
When Washington added Al-Nusra to its list of "terrorist" organisations, even the internationally-backed Syrian opposition National Coalition criticised the decision.
The Coalition's support for the group cooled after Al-Nusra officially pledged allegiance to Al-Qaeda chief Ayman al-Zawahiri and was named the group's official Syrian branch.
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But on the ground, almost all rebel groups have been willing to cooperate with Al-Nusra, seeing them as distinct from the Islamic State group (IS), which espouses transnational goals and includes many non-Syrians among its ranks.
Al-Nusra, by comparison, has maintained a focus on overthrowing Syrian President Bashar al-Assad -- the main goal of the rest of the Syrian opposition -- and has mostly Syrian fighters.
The cooperation between moderate and Islamist rebels and Al-Nusra has even extended beyond the fight against Assad to the creation of a coalition that began fighting IS jihadists in January.
Angered by its abuses against civilians and rivals, the loose coalition succeeded in pushing the group out of much of northern Syria, though it has since regained ground, bolstered by new recruits and weapons seized across the border in Iraq.
That history of cooperation has left some rebels and activists on the ground suspicious and even angry about the strikes on Al-Qaeda.
Ibrahim al-Idlibi, an activist in Idlib province, said the opposition backed strikes against IS, but not against Al-Nusra, or the so-called Khorasan.
"Some of these strikes only serve Western interests," he said.
Al-Nusra "has stood with the rebels against both Daesh and the regime," he added, using the Arabic acronym for IS.
- Tensions in US coalition? -
Many are also angry that the strikes are targeting jihadists but not the Syrian regime.
In a statement, the rebel Supreme Military Command affiliated with the opposition National Coalition emphasised "the need to avoid targeting moderate national and Islamic forces".
"We demand that the attacks focus on the forces of tyranny... represented by the Assad regime and its supporters."
And targeting Al-Nusra could even prove controversial within Washington's anti-jihadist alliance.
Some key members are believed to maintain channels of communication with Al-Nusra, including Qatar, which has helped negotiate the release of prisoners held by the group.
On Tuesday, Washington made clear that, unlike the strikes against IS, none of its allies participated in the raids against Al-Qaeda targets.
"These strikes were undertaken only by US assets," the Pentagon said.