Iraqi security forces in Baghdad are preparing for a major annual Shi'ite religious march, deploying additional police and banning cars from the streets until Saturday.
During the holiday, hundreds of thousands of Shi'ite pilgrims march to the shrine of Imam Moussa Kadhim, one of 12 major Shi'ite saints.
Religious processions in Iraq are frequently attacked by sectarian fighters.
On Wednesday, the U.S. military announced that troops killed 30 suspected militants and detained 12 others during raids on an alleged international bomb-smuggling network inside Baghdad's Shi'ite Sadr City neighborhood.
A military statement said the "Special Groups" terrorist network smuggled Iranian-made armor-piercing explosive devices and moved militants from Iraq to Iran for training.
Iraqi police said some of those killed in Wednesday's operation were civilians.
The raid came as Iraqi Prime Minister Nouri al-Maliki arrived in Iran for security talks.
U.S. officials have accused Iran of providing support for Shi'ite militants in Iraq. Tehran denies the charge and says the U.S. presence in Iraq worsens the country's insurgency.
Also Wednesday, the British Ministry of Defense said a British soldier was killed Tuesday in the southern Iraqi port city of Basra. The U.S. military said a roadside bomb killed a U.S. soldier in Baghdad Tuesday.
Some information for this report was provided by AP.
