The blasts in Karbala were the latest in nearly a week of attacks that have killed at least 159 people. The uptick in violence has shattered a lengthy period of calm and raised anew concerns about the readiness of Iraqi forces to take over their own security ahead of a full withdrawal by the U.S. military.
The first attack occurred about 7 a.m. in a parking lot near busloads of pilgrims on the eastern outskirts of Karbala, 55 miles (90 kilometers) south of Baghdad. Police and hospital officials said that six pilgrims were killed and 34 people wounded in that attack.
A second bomb was discovered nearby and dismantled before it could explode, police said.
More than four hours later, a second car bomb struck pilgrims on the southern edge of the city, killing at least 12 people, including 10 pilgrims and two soldiers, and wounding 21, the officials said.
There is a vehicle ban in Karbala for the holy period so pilgrims are dropped off at parking lots and walk in.
The police and hospital officials spoke on condition of anonymity because they were not authorized to release the information.
Monday's attacks followed a triple suicide bombing last week along two highways leading to Karbala that killed 56 and wounded at least 180 - most of them Shiite pilgrims.
Hundreds of thousands of pilgrims are gathering in Karbala for Monday's ceremonies marking the end of Arbaeen, a 40-day mourning period to observe the seventh century death of the Imam Hussein, the Prophet Muhammad's grandson.
His death in battle near Karbala sealed Islam's historic Sunni-Shiite split - the ancient divide that provided the backdrop for the sectarian bloodshed in Iraq after the 2003 U.S.-led war.
No group claimed responsibility for Monday's blast, but car bombs and suicide attacks are the trademark of al Qaeda in Iraq and other Sunni religious extremists.
Those groups have frequently targeted Shiites in a bit to re-ignite sectarian violence that pushed the country to the brink of civil war.
Since the end of Saddam's rule, Shiite politicians have encouraged huge turnouts at religious rituals, which were banned under the former regime, as a demonstration of Shiite power.
Security forces also have been targeted in the latest spate of violence, which began last Tuesday with a suicide bombing targeting police recruits in Tikrit.
The Islamic State of Iraq, an al Qaeda front group, has claimed responsibility for the Tikrit attack as well as two bombings last week at security force headquarters in Baqouba that together killed 10 people.
Also Monday, police said two bombs in Baghdad killed an Iraqi Army intelligence officer and his driver and wounded eight bystanders in separate strikes that hit a Shiite and a Sunni neighborhood. Hospital officials in Baghdad confirmed the fatalities.
A roadside bomb exploded near Tikrit as Salahuddin provincial Gov. Ahmed Abdullah al-Jubouri's motorcade was driving by, wounding five of his bodyguards, said police spokesman Col. Hatam Akram. The governor was not hurt in the blast near Saddam Hussein's hometown, some 80 miles (130 kilometers) north of Baghdad.
Violence has dropped dramatically in Iraq since the height of the war three years ago, but bombings and drive-by shootings still persist on a near daily basis.