Also Monday, the U.S. military said two soldiers were killed the day before in fighting in the Salahuddin province.
The statement did not give a precise location but the province includes Samarra, where insurgents attacked a U.S. outpost Sunday, triggering gun battles that ended when a U.S. jet bombed a house where gunmen had taken refuge. Iraqi officials said seven people, two of them children, were killed.
Iraqi security forces have mounted a major operation to protect Shiite pilgrims. Sunni religious extremists, including al Qaeda in Iraq, have launched massive and deadly attacks against pilgrims during Shiite celebrations in the past.
Despite the security measures, one pilgrim was shot on Baghdad's Jadiriyah bridge and gunmen hiding in an orchard south of the capital opened fire on another group, killing one and injuring three others.
Three more pilgrims were injured when gunmen attacked them in a drive-by shooting in southwestern Baghdad and police prevented another attack, defusing two roadside bombs planted along the route to Karbala in Musayyib, about 40 miles south of Baghdad, officials said.
More than a million Shiites from throughout the world were expected to converge on the Shiite holy city for the celebrations, which reach their high point late Tuesday and early Wednesday. The Shabaniyah festival marks the birth of Mohammed al-Mahdi, the 12th and last Shiite imam who disappeared in the 9th century.
Security concerns are running high, in part because of the political deadlock that has paralyzed the government only weeks before U.S. Ambassador Ryan Crocker and Gen. David Petraeus report to Congress on progress here since the arrival of an additional 30,000 U.S. troops.
Key Democrats including Sen. Hillary Clinton have called for Prime Minister Nouri al-Maliki to be replaced because his Shiite-dominated government has been unable to forge national unity.
In other developments: