Roadside bombs struck two minibuses filled with Shiite pilgrims returning to Baghdad on Monday, killing eight people and wounding 24 others, officials said, in the latest of a series of deadly attacks targeting the pilgrims.

The first bomb rocked a minibus pulling into a busy square in the Shiite neighborhood of Sadr City in Baghdad, killing four people and wounding 11 others, said a police official.

The driver, who refused to give his name, said his minibus was filled with pilgrims returning from the Shiite holy city of Karbala, 50 miles south of the capital.

The second minibus coming from Karbala was attacked in the Shiite neighborhood of al-Kamaliya in southeast Baghdad, killing four people and wounding 13 others, said the police official.

Medical officials confirmed the number of dead and wounded in the two attacks. All the officials spoke on condition of anonymity because they were not authorized to talk to the media.

The attacks followed a series of bombings last week targeting pilgrims on their way to Karbala that killed 60 people and wounded 170.

Hundreds of thousands of Shiite pilgrims converged on Karbala in recent days to celebrate the end of 40 days of mourning that follow the anniversary of the seventh-century death of one of Shiite Islam's most revered saints, the Prophet Muhammad's grandson Hussein.

Most of those pilgrims left Karbala early on Monday after the end of the religious ceremony, and the Iraqi government called on owners of private vehicles to help ferry them home.

The Iraqi government deployed more than 30,000 security personnel to protect the pilgrims, but the long distances that many Shiites travel to Karbala make it difficult to shield them from all attacks along the way.

Sunni militants have kept up their attacks against Shiites, hoping to re-ignite the kind of sectarian violence that engulfed the country two years ago.

But the Iraqi government has also stepped up its offensive against extremists throughout the country.

Iraqi Prime Minister Nouri al-Maliki launched several operations against Sunni and Shiite militants last year, including one in Sadr City to wrestle control from a militia led by radical Shiite cleric Muqtada al-Sadr.

The operations have helped reduce violence in Iraq to a five-year low and propelled al-Maliki's party to victory in provincial elections held throughout much of the country on Jan. 31.

Iraqi election officials plan to announce final results this week. But preliminary figures announced Feb. 5 indicate al-Maliki's ticket beat Shiite religious parties in Baghdad and southern Iraq, including its main rival, the Supreme Islamic Iraqi Council, which has close ties to Iran.

The Supreme Council won control of much of the south in the last provincial elections in 2005.

Humam Hammoudi, a senior member of the Supreme Council, said his party has set up a committee to look into the "surprise" results from the recent provincial elections.

"The way the election results turned out contradicted the forecasts and expectations," Hammoudi said in an interview published Monday in the pan-Arab Al-Hayat newspaper.

Hammoudi acknowledged the party's "ability to rally large numbers was not matched by others" but said "ugly" centralized policies from Baghdad were partly to blame for the perception that the Supreme Council did not perform well when it controlled the south.

The Supreme Council has lobbied to carve out a semi-autonomous region in the oil-rich south similar to the Kurdish-ruled area in the north — an idea that al-Maliki has strongly opposed.

Faraj al-Haidari, head of the country's election commission, said Sunday that Iraqi officials nullified provincial election results in more than 30 polling stations across the country due to fraud, but the cases were not significant enough to require a new vote in any province.

Another area where there has been controversy relates to certificates candidates needed to verify that they had at least a high school diploma so they can run.

Judge Raheem al-Ugaily, the head of Iraq's Public Integrity Commission, told The Associated Press on Monday that his group has discovered 258 forged certificates presented by candidates. More than 14,000 candidates ran for 444 council seats in 14 out of Iraq's 18 provinces in the Jan. 31 vote.

Abdul-Aziz al-Hakim, the head of the Supreme Council, criticized the election commission and demanded the group address cases of fraud before announcing final results.

"The results of the provincial elections were not accurate," U.S.-funded Radio Sawa quoted al-Hakim's son and heir apparent, Ammar, as saying in a speech delivered on behalf of his ailing father Sunday in Karbala.

The results "indicate fraud by influential parties in the election commission," he was quoted as saying.