A woman reacts while Security forces inspect the scene of a bomb attack on Shiite pilgrims, killing and wounding scores of people, police said, near the southern port city of Basra, Iraq's second-largest city, Jan. 14, 2012. (Nabil al-Jurani/AP)

A furious explosion ripped through a group of Shiite pilgrims Saturday near the southern Iraqi city of Basra, killing 53 in at least the eighth attack this year against Shiites making their annual treks to holy shrines, security officials said.

The blast was triggered by a suicide bomber disguised in a military uniform, said Lt. Col. Jassim Lefta, a provincial police official. At least three children were among the dead, he said.

Scores of Iraqi military and security forces have tried to protect the millions of pilgrims — many arriving from other countries — who walk to shrines south of the capital to honor a venerated martyr, Imam Hussein. Their 40-day mourning period ended Saturday.

Despite the stepped-up security, dozens of Shiites have been killed in this increasingly tense country in the month after the departure of U.S. troops. Explosions have rocked Sunni areas as well. Officials believe they are the work of terrorist groups that are trying to take advantage of ongoing sectarian political battles in hopes of provoking a return of the bloody fighting between Shiite and Sunni militants several years ago.

In interviews, the most common refrain of Shiite and Sunni citizens is that they care little about sectarianism and care a lot about jobs and having more than six hours of electricity a day.

In parts of the country Saturday, Shiite pilgrims had to walk through checkpoints and have their bags checked. After the explosion near Basra, though, survivors said security forces had not done enough, said Lefta, the security official.

Riyad Abdulameer, a health official in Basra province, put the number of dead at 53 and injured at 137.

The attack Saturday was similar to one Jan. 5, when a bomber on the outskirts of Nasiriyah detonated explosives near Shiite pilgrims, killing at least 48 people and wounding at least 81. Just before that bomb went off, an Iraqi army officer spotted the assailant and tried to intervene by wrapping his arms around him, said the area’s security chief, Sajad al-Asadi. The officer, a Sunni, was killed in the bombing and became a symbol of non-sectarian heroism across the country.

Anthony Cordesman, an analyst at the Center for Strategic and International Studies, said that “Iraq is still a long, long way from the point” where terrorists could provoke large-scale sectarian battles as they did several years ago. But he nevertheless worries that the split between Shiite and Sunni leaders could prompt militias on both sides to take up weapons. “Iraq needs more unified and effective leadership. And it needs it desperately,” he said.Security forces reported some gains. In the Diyala province, security forces captured eight wanted men. And in the city of Baqubah, a roadside bomb was discovered and eliminated.

The attacks could hurt Iraqi Prime Minister Nouri al-Maliki, a Shiite whose political coalition was built on the idea of security. “It is the very name of his coalition: State of Law,” said Lt. Col. Joel Rayburn, an Iraq analyst at the National Defense University who earlier served as a U.S. intelligence officer in the country, stressing that he was expressing his opinions and not those of the university. “His whole reputation is built on the claim that he can enforce the law.”

Elsewhere Saturday, a woman was killed and three people were injured when a bomb exploded beneath their taxi in Baghdad. A similar blast near Abu Ghraib killed two others. In Babil province, south of Baghdad, gunmen opened fire on a checkpoint, wounding three security officers. And in Waset, security forces found the corpse of a 9-year-old girl who had been kidnapped the day before.

Babak Rahimi, an Iraq expert at the University of California at San Diego, said Sunni extremists are likely striking out against what they perceive as a weak government — a perception formed by the factional rivalries in Baghdad that have become more pronounced since the U.S. troops left.

He struck a hopeful chord, saying that “new symbols of national, cross-sectarian unity are slowly emerging to challenge sectarian politics.”

Special correspondents Aziz Alwan, Asaad Majeed and Uthman al-Mukhtar contributed to this report.