IRBIL, IRAQ — The United State used a long-awaited aerial campaign against the Islamic State to hit a group of al-Qaida-affiliated jihadists who U.S. officials claim were planning attacks on Western targets.

In addition to hitting Islamic State targets in the Syrian cities of Raqqa, Deir el Zour, and Abu Kamal, the United States struck core al-Qaida members known as the Khorasan unit who’d joined the Nusra Front, the official al-Qaida franchise in Syria.

The Syrian Observatory for Human Rights said at least 50 Nusra fighters were killed in the attacks, which the U.S. Central Command said hit eight bases in western Aleppo province.

In a statement, the Central Command was careful to note that only U.S. planes participated in the attacks on the Nusra-Khorasan units. The United State identified five countries — Bahrain, Qatar, Saudi Arabia, Jordan and the United Arab Emirates — as having participated in the attacks on the Islamic State.

The “Khorasan” group operates as an external operations wing of the Nusra Front. One expert in jihadi movements said its purpose was to organize an attack on Western targets to help stem the tide of defections by jihadists from Nusra and its al-Qaida allies to the newer and more radical Islamic State after the Islamic State’s string of victories over the summer.

“It’s not a separate group from Nusra,” said Aymenn al Tamimi, who studies jihadist groups for the Middle East Forum, a Philadelphia based think tank. “The U.S. attempt to distinguish it is just a pretense for striking Nusra because they know Nusra has support on the ground and works with a wide range of rebel groups, some of whom the U.S. might want to consider aiding against IS.”

Muhsin al Fadhli, a top al-Qaida operative and financier, who was believed to be under house arrest in Iran before apparently moving to Aleppo, leads the unit, according to American officials. The U.S. government in October 2012 offered a $7 million reward for information that leads to his death or capture.

There was no information on whether he was specifically targeted in the raid but the Syrian Observatory for Human Rights, a pro rebel monitoring group, said medical sources in Aleppo reported that the strikes killed at least 50 Nusra fighters.

Tamimi said that the argument made by U.S. officials that the group, which is claimed to include top bomb makers and operational officials from the core al-Qaida group based in Pakistan, is planning an operation against the West makes sense as both al-Qaida and Nusra, al-Qaida’s official Syrian franchise, have been hit hard by a rash of defections of fighters to their rivals in the Islamic State. Nusra was once the Syrian branch of the Islamic State before the two groups split last year over command issues, and the Islamic State renounced the leadership of al-Qaida and top commander, Ayman al Zawahiri.

“Relevance is the concern for al-Qaida more generally,” Tamimi said “Namely, to prevent defections to the Islamic State, they need to attack the West to maintain credibility.”

But the attack by American forces on Nusra was likely to earn anger from more moderate Syrian rebel groups, which frequently coordinate with the al-Qaida affiliate in attacks aimed at the government of President Bashar Assad.

U.S. officials have been warning for the past two weeks about the dangers posed by Khorasan, with James Clapper, the director of national intelligence, telling a conference Sept. 18 that “in term of threat to the homeland, Khorasan may pose as much of a danger as the Islamic State.”

U.S. intelligence officials have disclosed few details about the group, whose head, Muhsin al-Fahdli, 33, a Tunisian reportedly was so close to bin Laden that he was among a small circle of followers told in advance of the Sept. 11, 2001, plot.

Some experts believed Fahdli was personally dispatched to Syria by Zawahiri, bin Laden’s successor as head of al Qaida, with the purpose of recruiting foreign fighters who could return to their homelands to stage attacks. Hundreds of Americans and Western Europeans have gone to Syria to fight for Nusra, the Islamic State and other Islamist groups.

Iran claimed it put the group, which included one of bin Laden’s sons and a son-in-law, under house arrest. But U.S. officials have said its members continued to plot attacks from Iran. Many ultimately left for other countries.

In 2005, former President George Bush said that Fahdli was involved in aiding terrorists who bombed a French oil tanks off the coast of Yemen in 2002.

The name Khorasan holds prophetic significance for many jihadis. It was the name of a region comprising parts of Iran, Afghanistan and Turkmenistan. Some Hadiths, or sayings attributed to the Prophet Mohammad, foretold of an army carrying the black banners of Islam that would ride out of Khorasan, sweeping all before it.

In all, the U.S. and its allies hit 14 Islamic State targets, Central Command said in its statement. The targets, Central Command said, “included ISIL fighters, training compounds, headquarters and command and control facilities, storage facilities, a finance center, supply trucks and armed vehicles.”

Forty-seven Tomahawk cruise missiles were launched from two ships, the USS Arleigh Burke and the USS Philippine Sea, which were in the Red Sea and the North Arabian Gulf, Centcom said. Aircraft came from the Air Force, Navy and Marine Corps.

Much of the first wave of air strikes targeted the Islamic State’s capital in the eastern Syrian city of Raqaa, which has been under complete control of the group since January and has been administered by the group since last year. In addition to the pragmatic delivery of social services, the group has imposed a regimen of brutal justice derived from early Islamic law that includes amputations, beheadings, crucifixions and public executions.

One local resident, who asked not to be identified out of fear of the Islamic State, said that although there were multiple air strikes on the several of the group’s most public facilities, which include commandeered Syrian government offices and other public buildings, there was not extensive damage to the city itself.

“It’s actually not that bad,” he said of the damage to non-Islamic State targets. “The strikes were very loud and surprising but did not seem to hit many civilian homes.”

Islamic State facilities throughout the city were hit, he said, but getting a close look at the damage was impossible, as fighters had deployed to the streets to prevent onlookers from assessing the damage.

“It’s very tense right now,” the resident said.