A suicide bomber attacked Shiite pilgrims north of Baghdad on Monday, killing at least 17 people, officials and a survivor of the blast said.
The attack in the Taji area, which targeted a tent serving refreshments to pilgrims, also wounded at least 35 people.
Pilgrims from Iraq and abroad are making their way to Samarra, north of Baghdad, to commemorate the death of Hassan al-Askari, one of the 12 revered Shiite imams, who is buried in the city.
"We were distributing food, fruit and tea to the pilgrims who were walking to Samarra, and a suicide (bomber) blew himself up," Sajjad, 25, said at a Baghdad hospital where his brother Mustafa was being treated for shrapnel wounds.
The bomber carried a Shiite flag as a disguise and yelled "Allahu akbar" (God is greatest) before detonating the explosives he carried, Sajjad said.
There was no immediate claim of responsibility for the attack, but suicide bombings are almost exclusively carried out by Sunni extremists in Iraq, including the Islamic State group.
IS spearheaded a June offensive that overran large parts of the country, and Iraqi security forces, Kurdish fighters and Shiite and Sunni militiamen are battling to push the militants back.
A US-led coalition is carrying out air strikes against IS in Iraq and Syria, and also providing training to Iraqi forces.