U.S. Jets Strike at Khorasan Militant Group in Syria BAGHDAD - American fighter jets carried out a series of airstrikes in northwestern Syria on Thursday that sought to kill leaders of a Qaeda-linked militant cell that is plotting attacks on the West, American officials said. American intelligence assessments call the group Khorasan and say it could pose a more immediate threat to the United States and Europe than the Islamic State, which has seized territory on both sides of the Iraq-Syria border. While a United States-led coalition has frequently bombed the Islamic State in Syria and Iraq, it had not targeted Khorasan since hitting its bases with a barrage of cruise missiles at the start of its campaign in Syria on Sept. Of greatest interest to the United States government is Muhsin al-Fadhli, a Kuwaiti who is said to have founded Khorasan in Syria and was a senior Qaeda operative close to Osama bin Laden. After the strikes in September, American officials expressed optimism that the missile barrage had killed at least some of Khorasan's leaders, including Mr. Fadhli. Some jihadist sympathizers hailed him on social media as a "martyr." But in recent weeks, as intelligence analysts sifted through field reports and communications intercepts, they grew more certain that senior members of the group had survived. "The Khorasan group, we still believe, remains a dangerous entity, that they still have desires and designs to attack Western targets," Rear Adm. John Kirby, the Pentagon press secretary, told reporters this week. Admiral Kirby declined to comment on the status of Khorasan's leadership. In a statement after Thursday's strike, the United States Central Command, which oversees military operations in the Middle East, said that initial reports indicated that the strikes had succeeded in "destroying or severely damaging several Khorasan group vehicles and buildings assessed to be meeting and staging areas, I.E.D.-making facilities and training facilities." The statement did not mention the targeting of any individuals. Syrian activists also reported the strikes, saying that they had killed at least two children and an unknown number of fighters. One hit a car belonging to the Nusra Front in the village of Sarmada. The activists did not say who had been in it. Other strikes hit facilities belonging to the Nusra Front in the town of Harim, reducing them to rubble, and a base belonging to another Islamist rebel group, Ahrar al-Sham, near a border crossing with Turkey. In statements and photos posted online, Ahrar al-Sham and the Nusra Front acknowledged that their bases had been hit. The Syrian Observatory for Human Rights, an antigovernment monitoring group, said that two young girls had been killed in the strike on Harim and that six members of the Nusra Front had been killed in another strike in Aleppo Province farther east. Another activist, who gave his name as Ibrahim al-Idlibi, said seven civilians had been killed in addition to a number of fighters from Ahrar al-Sham. Many in the Syrian opposition have expressed skepticism about the existence of the Khorasan group, saying that the United States had created it to justify strikes on Islamist rebels. Some also defend the Nusra Front, calling it a loyal ally in the fight against President Bashar al-Assad. All the strikes on Tuesday occurred in the ungoverned strip of land along the Turkish border, where many rebel groups have bases and frequently go to Turkey to buy supplies and to take a break from the war. Membership in many of these groups is fluid, with fighters flowing among them based on who has arms and money. The United States has been providing limited arms support to a small number of rebel groups deemed to be moderates, and a larger plan to train 5,000 rebels a year to fight the Islamic State is in the planning stages. But that support has fueled tensions between its recipients and Islamist groups like the Nusra Front, which has been expanding its control in Idlib Province at the expense of other groups. In its statement, Central Command said that Khorasan was linked to the Nusra Front, but that the strikes were not in response to the Nusra Front's clashes with other rebels and did not target the Nusra Front "as a whole."