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Cook said the strikes were approved by President Obama upon the recommendation of the chairman of the Joint Chiefs of Staff and the U.S. secretary of defense.
One video shows the first U.S. airstrike, which targeted an ISIS tank in Sirte, Libya. In a press release with the video, the Department of Defense said the strike “successfully disabled” the T-72 tank being used by ISIS militants.
Another video shows an AV-8B Harrier fighter jet taking off from the flight deck of the USS Wasp to conduct a strike mission over Sirte. The fighter jet is a member of the North Carolina-based Marine Medium Tiltrotor Squadron 264, nicknamed the “Black Knights.”
Almost all U.S. and coalition strikes against ISIS up to this point have been conducted inside Iraq and Syria. But ISIS is known to have a presence in Libya as well. These strikes, Cook said, will help Libyan government forces build on some of the success they have already had in recapturing territory from ISIS around Sirte.
Cook also signaled in his statement that the strikes represent the first of a broader campaign in Libya: “Additional U.S. strikes will continue to target ISIL in Sirte in order to enable the [Libyan government] to make a decisive, strategic advance." Cook said the pace and duration of the campaign will depend on what the Libyan government requests.
ABC News' Justin Fishel contributed to this report.