Thursday's bombings come one day after 53 people were killed, including 32 at a Shiite funeral east of Baqouba.
The suicide blast near the Imam Hussein shrine in central Karbala, 80 kilometers (50 miles) south of Baghdad, killed 49 people and injured 52, Karbala police Col. Razaq al-Taie.
Pools of blood lay at the blast site, and television images showed men ferrying the wounded in pushcarts. The bomber appeared to have set off the explosion only about 30 meters (30 yards) from the shrine in a busy pedestrian area surrounded by shops.
A suicide bomber blew himself up outside a police recruiting center in the restive city of Ramadi, killing at least 30 people and injuring another 40, police and hospital officials said.
The attack happened at a police screening center in Ramadi, an insurgent stronghold 70 miles west of Baghdad. At least 30 people were killed, said Mohammed al-Ani, a doctor at Ramadi General Hospital and police Capt. Nassir al-Alousi.
The U.S. military did not have a casualty figure, but said that a suicide bomb exploded at 10:55 a.m. near the Ramadi Glass and Ceramics Works "where screening for Iraqi Police Officers was taking place."
Karbala has been relatively free of violence since December 2004, when seven people were killed and 31 wounded in an attack. In March of that year coordinated attacks from suicide bombers and preset explosions on Karbala's holy sites killed more than 100.
Wednesday, a suicide bomber killed 32 mourners and wounded dozens at a funeral for the nephew of a Shiite politician, one of several attacks across Iraq that killed a total of 53 people — making it the deadliest day since the Dec. 15 elections.
The increased violence came as Iraq's three major political parties were close to forming a coalition government that would include Shiites, Sunni Arabs and Kurds, according to a Shiite politician.
Iraq's election commission said it planned to release the results of its investigation into almost 2,000 complaints stemming from last month's parliamentary elections within the next two days.
In other developments:
More than 100 mourners were standing in a cemetery in Muqdadiyah, about 60 miles north of Baghdad, for the burial of a nephew of Ahmed al-Bakka when the bomber struck, the Diyala provincial police said. The cemetery was strewn with body parts and the tombstones were stained with blood.
At least 32 people were killed and 42 wounded, said Dr. Firas al-Nida of the Muqdadiyah hospital.
Al-Bakka had survived an assassination attempt Tuesday that killed his nephew. Al-Bakka is the head of the local Dawa party, led by Prime Minister Ibrahim al-Jaafari and a main partner in the country's largest Shiite political coalition, the United Iraqi Alliance.
Shiites have been targeted by extremist Sunni groups such as al Qaeda in Iraq, led by Jordanian-born terrorist mastermind Abu Musab al-Zarqawi.