Iraqi officials say gunmen have killed at least 16 Shi'ite pilgrims as they gathered for a major religious event in Baghdad.
They say more than 200 people were wounded when gunmen fired on pilgrims as hundreds of thousands of people marched to a Shi'ite shrine in Kazimiyah.
Iraqi officials say police captured at least three gunmen.
Sunday's pilgrimage commemorates the death of eighth-century Imam Moussa Kadhim. He is buried in a tomb in Kazimiyah.
Iraqi authorities banned vehicles from Baghdad streets until after the pilgrimage ends this evening to try to stop Sunni insurgents from targeting Shi'ites with car bombs.
During last year's pilgrimage, almost 1,000 Shi'ites died in a stampede on a bridge over the Tigris River, sparked by false rumors of a suicide bomber in the crowd.
Iraqi Prime Minister Nouri al-Maliki warned that anyone who uses a mosque to incite sectarian violence during the pilgrimage will be prosecuted under anti-terror laws.
Today's march is taking place as American and Iraqi forces continue their large security operation in the Iraqi capital aimed at curbing sectarian violence.