A security operation is under way in Baghdad to protect tens of thousands of Shia pilgrims who are converging on the Kadhimiya mosque in northern Baghdad.
Authorities in Baghdad have ordered a three-day curfew banning all vehicles from yesterday morning. Shops were shuttered throughout the city, and streets away from the pilgrimage route were deserted.
The pilgrimage followed a day of angry funerals in Baghdad's Shia slum of Sadr City, where the United States said it had killed an estimated 30 militants it claimed were linked to Iran.
The annual pilgrimage, in honour of one of the 12 imams revered by Shia, has attracted one million people or more in the years since the fall of Sunni Arab ruler Saddam, with many making their way from the far south of the country.
The ceremony has been marred by violence in recent years.
Two years ago, nearly 1,000 pilgrims were killed in a stampede on a bridge near the shrine sparked by rumours of a suicide bomber, the single most deadly incident since the US-led invasion in 2003.
Last year gunmen ambushed pilgrims on the way to the shrine, killing 20 and wounding 300.