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The U.S. military launched an airstrike that targeted and "likely" killed an Al Qaeda leader behind the attack on a gas plant in Algeria in 2013 that killed 35 hostages, including three Americans, a senior defense official told Fox News Sunday.

However, an Islamist with ties to Libyan militants told the Associated Press that the airstrikes missed Mokhtar Belmokhtar, instead killing four members of a Libyan extremist group the U.S. has linked to the Sept. 11, 2012, attack on the U.S. Consulate in Benghazi that killed Ambassador Chris Stevens and three other Americans.

Libyan government and U.S. officials say warplanes targeted BelMokhtar and several others in the eastern city of Ajdabiya. The U.S. filed terrorism charges against BelMokhtar last year in connection with the Algeria attack. Officials have said they believe he remained a threat to U.S. and Western interests.

The Libyan government in a statement said that the strike came after consultation with the U.S. so that America could take action against a terror leader there. Neither U.S. officials nor the Libyan government provided proof of Belmokhtar's death, which likely requires a DNA test or an announcement by Belmokhtar's group that he was killed.

One government official in Libya said an airstrike in Ajdabiya hit a group believed to be affiliated with Ansar al-Shariah, and that it killed five and injured more. He said the group that was injured got into clashes with the Libyan military that guarded the hospital there, leading to hours of fighting. He spoke on condition of anonymity because he was not authorized to speak to reporters.

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    The Islamist, who spoke to AP anonymously for fear of retaliation, said that the four killed in the strike were members of Ansar al-Shariah and added that Belmokhtar wasn't at the site. It was not immediately clear whether the Islamist and the Libyan official were describing the same airstrike.

    A senior U.S. defense official told Fox News that a manned U.S. warplane targeted BelMokthar. A U.S. official told the AP two F-15 fighter jets launched multiple 500-pound bombs in the attack. Authorities say no U.S. personnel were on the ground for the assault.

    The charges filed against Belmokhtar by federal law enforcement officials in Manhattan included conspiring to support Al Qaeda and use of a weapon of mass destruction. Additional charges of conspiring to take hostages and discharging a firearm in furtherance of a crime of violence carry a maximum penalty of death.

    At the time, U.S. Attorney Preet Bharara said in a release that Belmokhtar "unleashed a reign of terror years ago, in furtherance of his self-proclaimed goal of waging bloody jihad against the West."

    Authorities also offered a $5 million reward for information leading to the arrest of Belmokhtar, who's also been known as "the one-eyed sheik" since he lost an eye in combat. Belmokhtar recently left Al Qaeda in the Islamic Maghreb, the North African offshoot of the terrorist group, then formed his own spinoff.

    The weekend strike is not the first time the U.S. has gotten involved in tracking down militants in Libya. In 2013, U.S. special forces went into Tripoli and seized Abu Anas al-Libi, whisking him out of the country. Al-Libi was accused by the U.S. of involvement in the 1998 bombings of two American embassies in Africa. Al-Libi died January this year in a US hospital from a long-standing medical condition.

    The airstrike comes as Al Qaeda militants in eastern Libya continue to battle with members of the Islamic State (ISIS), as the warring groups fight over power and resources.

    Last week, a senior Al Qaeda leader was killed by masked gunman, prompting the group to declare holy war on the local ISIS affiliate. Clashes between the two groups in the eastern coastal city of Darna killed 11 people.

    Libya has been divided between an Islamist-led government backed by militias that seized the capital of Tripoli last August and its elected parliament, which now must convene in the far east of the country.

    Militants have taken advantage of the chaos, flowing fighters into the country's vast ungoverned spaces. And as ISIS has grown in power, fueled by successes in Iraq and Syria, some Al Qaeda fighters have switched loyalties.

    In its statement Sunday, the Libyan government said that the operation "is a piece of the international support that it has long requested to fight terrorism that represents a dangerous threat to the regional and international situation." It added that the government would like more help fighting terrorism, including ISIS, which controls Sirte and is moving west toward Misrata and south toward the Jufra military base.

    Fox News' Lucas Tomlinson, Jennifer Griffin and The Associated Press contributed to this report.