Mr. Baghdadi, in a 33-minute speech posted Sunday on a Web site often used for messages by Al Qaeda, promised that a new offensive, which he called Breaking Down Walls, would begin soon. He described the impending campaign as part of a battle by Sunnis against Iraq’s Shiite leaders and people.

Image Attacks by Al Qaeda in Iraq covered a wide area. Credit... The New York Times

He also heaped praise on the Syrian insurgents, declaring, “You have taught the world lessons in courage, jihad and patience,” according to a translation by the SITE Institute, a Washington group that tracks Islamic extremism on the Internet. It quoted him as saying the anti-Assad fighters in Syria had rendered the Syrian president and his allies “terrorized by the future of your volcano.”

The offensive, coming in the early days of Ramadan, the monthlong religious rite of fasting by day and feasting by night, was without precedent over the past few years, at least in the sheer number of attacks, spread over so many locations in a third of Iraq’s 18 provinces, from north to south.

It raised new concerns about the government’s ability to contain the violence, six months after the last American troops left the country following more than eight years of occupation and civil war that upended Saddam Hussein’s Sunni-led minority power base and empowered Iraq’s long-repressed Shiite majority.

“I think Al Qaeda in Iraq made a big joke of the government and the Iraqi security forces,” said Khalid Fadel, a military analyst and former instructor at the Iraqi Military College. “They were so clear that they were going to launch attacks during Ramadan, and the government said that they have information of about 30 terrorist groups entering the country, but still the security forces are unable to prevent the attacks.”