BAGHDAD, Iraq (CNN) -- Iraqi and coalition troops overnight killed about 30 people in Baghdad's Sadr City -- most of them in an airstrike -- as they targeted a militia cell with suspected links to Iran, the U.S. military said.
Twelve suspects were detained in the raid.
The Iraqi Interior Ministry said at least 11 people were killed and 15 wounded in the same violence in the sprawling Shiite slum.
Iraqi hospital and police officials said civilians were killed in the raid, but the U.S. military said civilians were not among the dead, Reuters reported. Watch ruin in wake of night of fighting »
"There were women and children in the area when we conducted the operation but none were killed in the airstrike," Army Lt. Col. Christopher Garver said, according to Reuters.
In the background of the violence, tens of thousands of Shiites were walking on their annual pilgrimage to the Kadhimiya shrine in northwest Baghdad; Iraqi Prime Minister Nuri al-Maliki traveled to neighboring Iran; and an international meeting was held in Damascus, Syria, dealing with border security in Iraq.
Shiite-dominated Iran has strong support in Sadr City, the headquarters of the Mehdi Army, the militia that aligns itself with populist anti-American cleric Muqtada al-Sadr.
The Interior Ministry official said elements of the Mehdi Army were involved in Wednesday's fighting.
Al-Sadr agreed to rein in the Mehdi Army as a U.S.-Iraqi security crackdown began February 14, but some fighters have broken away from his control, according to The Associated Press.
The terrorist cell targeted Wednesday is suspected of bringing armor-piercing bombs called explosively formed penetrators from Iran to Iraq and of bringing militants from Iraq into Iran for terrorist training, the U.S. military said.
A senior U.S. military commander on Wednesday said 79 U.S. troops were killed in 99 armor-piercing bomb attacks in July, the highest monthly toll since counting began in December.
In Tehran, al-Maliki was to meet with the top leaders of the country, including Supreme Leader Ayatollah Ali Khamenei and President Mahmoud Ahmadinejad, according to Iran's Islamic Republic News Agency.
Al-Maliki's office said he met with Iranian Vice President Pervez Dawoodi on Wednesday. They discussed security and energy projects.
In Damascus, Syria, representatives from Iraq, its neighboring countries and the permanent members of the United Nations began a two-day session on Iraq's border security.
The meeting is the third in a series of sessions to emerge from the Iraqi neighbors' conference earlier this year at Sharm el-Sheikh in Egypt, said Tom Casey, deputy State Department spokesman.
The violence in Baghdad came during a trying week for security forces, who are attempting to protect tens of thousands of Shiites walking to the Kadhimiya shrine in northwestern Baghdad to commemorate the death of Musa al-Kadhim, an eighth-century imam.
Iraq's government moved up a vehicle ban for Baghdad from 10 p.m. to 5 a.m. Wednesday to deal with the influx. An Iraqi official said the vehicle ban, which was imposed 17 hours earlier than expected, surprised residents who were headed to work and told by Iraqi security forces to return home.
Two years ago, the throngs headed to the mosque for the same commemoration panicked when rumors spread of a suicide bomber in their midst. The panic led to a stampede that killed nearly 1,000 people.
CNN's Barbara Starr contributed to this report.