Iraqi insurgents unleashed a string of bombings and other attacks primarily targeting the country's Shiite community on Saturday, leaving at least 40 dead in a challenge to government efforts to promote a sense of stability by preventing attacks during a major Muslim holiday.

The bloodshed appeared to be the worst in Iraq since Sept. 9, when insurgents launched a wave of bombings and other attacks that left at least 92 dead in one of the country's bloodiest days this year.

The attacks underscored the difficulties facing the country's leadership as it struggles to keep its citizens safe. Authorities had increased security in hopes of preventing attacks during the four-day Eid al-Adha celebrations, when people are off work and families gather in public places.

The deadliest attacks struck in the evening in the Shiite neighborhood of Sadr City. Police said a car packed with explosives blew up near a market, killing 12 people and wounding 27. Half an hour later, a second car bomb went off in one of Sadr city's bus stations, killing 10 and injuring 31.

Earlier in the day, a bomb exploded near playground equipment that had been set up for the holiday in a market on the capital's outskirts in the eastern neighborhood of Bawiya. Police officials said eight people were killed, including four children. Another 24 people, including children, were wounded, they added.

"Nobody expected this explosion because our neighborhood has been living in peace, away from the violence hitting the rest of the capital," said Bassem Mohammed, a 35-year-old father of three in the neighborhood who was startled by the blast.

"We feel sad for the children who thought that they would spend a happy time during Eid, but instead ended up getting killed or hurt."

Authorities have said they planned to increase the number of checkpoints, shut some roads and deploy extra personnel during the holiday period.