Explosions killed at least 26 people across Iraq on Thursday, most of them Shiite pilgrims taking part in a holy mourning ceremony, authorities said, raising fears of further sectarian attacks at the approach of Shiite Islam's most solemn occasion.

The deaths came three days before the climax of Ashoura, when hundreds of thousands of Shiite pilgrims converge on the central city of Karbala to mourn the killing of the Prophet Muhammad's grandson, Imam Hussein, in a 680 A.D. battle that sealed the split between Shiites and Sunnis.

While Thursday's attacks were smaller than similar bombings in previous years, they demonstrate that insurgents continue to incite sectarian tensions.

First came news of twin explosions targeting Shiite Muslim pilgrims in a central Iraqi town. The bombs killed at least 13 people and injured 74 others, authorities said.

Police Maj. Muthana Khalid said the first bomb exploded around 2 p.m. Thursday in Hillah, the capital of Babil province, about 60 miles (95 kilometers) south of Baghdad. He said the second explosion there came as police rushed to the scene 15 minutes later, a common tactic used by insurgents to maximize casualties.

"As people gathered here a powerful blast took place. A bomb exploded there and a car bomb exploded here," said eyewitness Ali Hussein.

The bombs targeted Shiite pilgrims who had gathered near a bus station in downtown Hillah, which is about 25 miles (40 kilometers) southeast of Karbala. People from around southern Iraq, which is overwhelmingly Shiite, make up the bulk of pilgrims traveling to Karbala.

A wrecked car lay at the attack site, and a pair of blood-covered slippers could be seen near damaged storefronts.

Among the dead was provincial councilman Nima Jassim al-Bakri, who was also a doctor, several authorities and a colleague said.

Khalid, the police spokesman, and Hillah councilman Iskandar Witwit said al-Bakri was driving to the attack site but was shot by a guard after he failed to stop at a checkpoint and the guard thought he was an attacker, Khalid and Witwit said.

At the second incident, in Baghdad, a bomb targeting a funeral killed nine and wounded 33 in Sadr City, a predominantly Shiite neighborhood, police and hospital officials said. They spoke on condition of anonymity because they were not authorized to speak to media.

The attack on the funeral procession raised questions about whether whoever planted the bomb thought they were targeting an Ashoura procession.

Then in a southern Baghdad neighborhood, a bomb killed four Shiite pilgrims and wounded 10 others on their way to Karbala, police and hospital officials said.

The 10-day period leading up to Ashoura is marked by processions through streets and Shiite neighborhoods across Iraq in which devout Shiites beat themselves with swords and other instruments as a way to show their devotion and mourning for Imam Hussein.

The mourning period usually takes place under heavy security, and this year was no different. The Iraqi government assigned more than 25,000 police and soldiers to protect pilgrims during the celebrations.

"The government is very aware of the threats to Christians and the Muslims" observing Ashoura, said U.S. Army Maj. Gen. John Johnson, a deputy commander in Iraq.

Violence in Iraq has dramatically declined since the insurgency pushed the country to the brink of civil war two years ago, but insurgents still regularly target security forces and civilians.

The Shiite event was banned under former dictator Saddam Hussein and his minority Sunni government. But the majority of Iraq's roughly 29 million people are Shiites, and the mourning period gained renewed prominence after Saddam's ouster and a Shiite-led government came to power.

But the potent symbol of religious grief has made a powerful target for Sunni insurgents intent on ripping the country apart. In 2008, a homicide bomber blew himself up among Shiite pilgrims in Iskandariyah, killing at least 40 people.

As authorities have fortified the area in and around Karbala, extremists have moved their efforts to pilgrims traveling relatively unprotected from outside Karbala.

"There is an investigation under way with those careless security men who did not perform well in search and checking," Hillah police chief Maj. Gen. Fadhil Radad told Iraq's state-run TV station.

Although Ashoura is essentially a mournful occasion, Iraq's majority Shiites have also used it to showcase their dominance after decades of oppression under Saddam, turning out in large numbers to mark the occasion despite the threat of insurgent attacks.