(WASHINGTON) -- The overnight airstrikes that hammered ISIS targets in Syria concluded with a pair of daylight raids that spotted and then destroyed a couple of armed ISIS vehicles, Pentagon officials said Tuesday.
The final shots of Monday's barrage were fired by U.S. warplanes about 9 a.m. in Syria (2 a.m. ET), officials said Tuesday.
The air raids have bombed about 20 targets inside Syria.
In addition, officials said that the targeting of a little-known off-shoot of al Qaeda was carried out because it was in the final stages of launching a terror attack on the U.S. homeland or Europe.
At the Pentagon briefing Tuesday morning, senior military officials described Monday night's airstrikes as the "beginning" of a sustained air campaign against ISIS in Syria.
"Last night's strikes are the beginning of a credible and sustainable persistent campaign to degrade and ultimately destroy ISIL," said Lt. General William Mayville Jr ., the director of Operations for the Joint Staff.
Mayville used an alternate name for ISIS, which also calls itself the Islamic State.
Mayville also predicted that ISIS will adapt to the new airstrike campaign and maintain a lower profile. He also described ISIS as a "learning organization...and they will adapt to what we've done and seek to address their shortfalls and gaps in our air campaign in the coming weeks."
Initial indications are that the airstrikes were "very successful," said Pentagon Press Secretary Rear Admiral John Kirby.
He described the participation of five Arab nations in Monday night's airstrikes against ISIS "as a critical part of our strategy."
Fighter aircraft from Jordan, the United Arab Emirates, Bahrain, and Saudi Arabia participated in Monday night's airstrikes, Qatar played a supporting role in the airstrikes.
The overwhelming majority of the munitions dropped over Syria in the airstrikes were from U.S. aircraft.
Monday's airstrikes also targeted the Khorasan Group, an off-shoot of al Qaeda that has concerned U.S. security officials because of its plans to conduct attacks against the U.S.
"We've been watching this group closely for some time," said Mayville. "We believe the Khorasan group was nearing the execution phase of an attack either in Europe or the homeland. We know that the Khorasan group has attempted to recruit Westerners to serve as operatives or to infiltrate back into their homelands."
Mayville said the group's attention was clearly not directed at the Assad regime or helping the Syrian people. They are "establishing roots in Syria in order to advance attacks against the West and the homeland."
Khorasan targets near Aleppo were struck in the first wave of airstrikes that included 47 Tomahawk cruise missiles launched from two U.S. Navy vessels, officials said.
"The majority of the Tomahawk strikes were against Khorasan Group compounds, their manufacturing workshops and training camps," said Mayville.
Mayville also said "we are unaware of any civilian casualties" and noted the U.S. takes the prevention of civilian casualties very seriously.
"And if any reports of civilian casualties emerge, we will fully investigate them," he added.
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