At a briefing for reporters, military officials showed photographs and video of before and after shots of the targets hit in Syria. In one case, the military bombed what officials said was an Islamic State finance center in Raqqa, targeting and destroying electronic and communications equipment on the roof, while leaving the rest of the building intact.

In another instance, American F-22 fighters targeted an Islamic State command and control building, hitting the right side of the structure, which officials said the Sunni militants were using for communications, storing weapons and holding meetings, while leaving the rest of the building intact.

General Mayville told reporters that the strikes were the beginning of a “credible and sustainable” campaign to destroy the Islamic State. He and other officials said that the hope is to limit civilian casualties by using precision strikes. American officials are also hoping to counter any attempt by the Islamic State’s formidable propaganda arm to accuse the United States and its allies of killing civilians.

A Pentagon official said Tuesday that with the exception of the Tomahawk cruise missiles, all of the strikes were launched from aircraft inside Syrian airspace. But officials declined to say whether the American military jammed Syria’s air defense system or whether the Syrian president, Bashar al-Assad, simply decided to allow the coalition warplanes into the country’s airspace.

When asked, General Mayville said that Syria’s air defenses were “passive” during the strikes.

While the airstrikes are the opening wave in what officials say will be a sustained air campaign, military analysts say the weak link in the strategy for combating the Islamic State remains the ability to train and equip Iraqi forces and Syrian rebels. It will take time to build up forces in both countries that will be strong enough to capture and hold territory from the militants.

In Iraq, American advisers need to train the 26 Iraqi brigades that the Pentagon says are still intact and loyal to the government and help the Iraqis establish new national guard units, which would have the primary responsibility for defending Sunni-dominated provinces and would be recruited largely from Iraqi tribes.