The attacks were predicted Sunday in an audio message attributed to the leader of Al Qaeda in Iraq, Abu Bakir Al Baghdadi, and posted on the group’s Web site. The message promised that a new offensive, which it called Breaking Down Walls, would begin soon.

In sheer number of attacks, the offensive was without precedent this year and was sure to raise concerns about the government’s ability to contain the violence six months after the last American troops left the country.

“We are returning again to dominate territories we used to dominate, as well as more,” Mr. Baghdadi said in the Qaeda statement. He depicted the attacks as part of a battle launched by Sunnis against the country’s Shia leaders.

The first attack came about 5 a.m. on Monday when gunmen stormed onto an Iraqi military base near the town of Duluiyah in Salahuddin Province and killed 15 Iraqi soldiers, according to security officials. Four soldiers, including a high-ranking officer, were wounded, and a fifth was taken prisoner by the insurgents, who escaped with him.

Then, in steady succession, mostly between 6 a.m. and 10 a.m., car bombs were set off across the country, from Taji and Husseiniya north of Baghdad, to Sadr City in eastern Baghdad; in Tuz in western Salahuddin Province, Dujail in southern Salhuddin, and Balad, northeast of the capital, according to police, hospital and Iraqi Army officials. Bombs also were set off in the northern cities of Mosul and Kirkuk, and in Diwaniya Province in the south.

The insurgents also attacked the home of a police official in Balad, seriously wounding four family members, and ambushed a checkpoint near Baquba, killing one policeman. In all, attacks were reported in at least five provinces.

Eight attacks were launched in Kirkuk Province, mostly targeting police patrols, with five people killed and 42 wounded.

The offensive started on the third day of the Islamic holy month of Ramadan, and apparently took advantage of the widespread practice in Iraq and many other Muslim countries of staying up most of the night, and then sleeping late during the daytime when fasting is required.

The attacks were likely to continue the trend of the first six months since the departure of American troops, when violence has steadily increased, according to United Nations statistics. June was one of the deadliest months so far, with about 200 people, mostly civilian pilgrims, reported killed.

American and Iraqi officials have argued that violence has been declining.

Unusually, only one of the attacks was attributed to a suicide bomber, in Mosul, where police managed to shoot him before he could cause any fatalities, authorities said. Authorities in Salahuddin Province, which seemed to be the worst hit area, said they also managed to defuse two car bombs and three roadside bombs without harm.

In Diwaniya, a car bomb exploded in a busy vegetable market, killing 5 people and wounding 32. A crowd at the scene became incensed and started smashing police cars, then marched on government buildings in the area, leading the police to fire on the crowd, killing one protester and wounding dozens of others, according to a police official.