ZUBAIR, Iraq -- An Iraqi health official says the death toll from a bomb attack on Shiite pilgrims near the southern port city of Basra has risen to 53 people.
The head of the Basra provincial health directorate Dr. Riyadh Abdul-Amir says hospitals received 53 killed and 137 wounded after the blast. He says some of the wounded are in serious condition, and warns the death toll may rise further.
The explosion was the latest in a series of attacks during Shiite religious commemorations that threaten to further increase sectarian tensions.
The attack occurred near the town of Zubair as pilgrims marched toward a Shiite shrine on the outskirts of the town.
The governor of Basra province's spokesman, Ayad al-Emarah, said it was not clear whether the blast was caused by a suicide attacker or a roadside bomb.
But Reuters says it was a suicide bomb attack.
Zubair is a predominantly Sunni enclave in Iraq's largely Shiite south.
The explosion came as Shiites commemorate the climax of Arbaeen, which marks the end of 40 days of mourning following the anniversary of the death of Imam Hussein, a revered Shiite figure.
Majid Hussein, a government employee, was one of the pilgrims heading to the shrine. He said people began running away in panic when they heard a loud explosion.
"I saw several dead bodies and wounded people, including children on the ground asking for help. There were also some baby strollers left at the blast site," he said.
The attack, which bore the hallmarks of Sunni insurgents, is the latest in a series of deadly strikes in this year's Arbaeen. Scores of pilgrims have been killed.
The largest of the Arbaeen attacks a wave of apparently coordinated bombings in Baghdad and outside the southern city of Nasiriyah killed at least 78 people on Jan. 5. It was the deadliest strike in Iraq in more than a year.
The attacks raise fears of a new sectarian rift that could destabilize the country now that U.S. troops are gone.
The last U.S. combat troops left Iraq on Dec. 18, ending a nearly nine-year war. Many Iraqis worry that a resurgence of Sunni and Shiite militancy could follow the Americans' withdrawal. In 2006, a Sunni attack on a Shiite shrine triggered a wave of sectarian violence that pushed the country to the brink of civil war.
Just as the American troops were leaving, a political crisis erupted that has paralyzed Iraq's government. It pits the country's mostly ethnic- and religious-based political blocs against one another.
Iraq's Sunni minority dominated the government under the dictatorship of Saddam Hussein, but since he was overthrown, Shiites have controlled most key posts.
The political dispute appears far from being resolved.
On Friday, Deputy Prime Minister Saleh al-Mutlaq called for Iraq's leader, Prime Minister Nouri al-Maliki, to step down or face a parliamentary vote of no-confidence. Al-Mutlaq's Sunni-backed Iraqiya party has been boycotting parliament and Cabinet meetings since last month to protest what it sees as efforts by al-Maliki to consolidate power, particularly over state security forces.
Al-Maliki's government, meanwhile, has demanded the arrest of the country's top Sunni politician, Vice President Tariq al-Hashemi of Iraqiya, accusing him of running a hit squad targeting government officials. Al-Hashemi denies the allegations.