BAGHDAD, Iraq (CNN) -- Three U.S. soldiers were killed when their base in Basra was attacked by indirect fire, the U.S. military said Friday.
They were killed Thursday night at the Contingency Operating Base in the southern Iraqi city, the military said.
The soldiers' names are being withheld until their families are notified, it said.
Also Friday, at least 30 Shiite pilgrims were wounded in four bombings targeting them as they made their way to a northern Baghdad shrine, an Interior Ministry official said.
Early in the day, a bomb under a bridge in Baghdad's New Baghdad district exploded, wounding at least 13 pilgrims, the official said, and two roadside bombings in two areas of southern Baghdad wounded another 13 pilgrims.
Early Friday afternoon, a parked car bomb detonated in Yousifiya, south of Baghdad, wounding at least four pilgrims, the official said.
Earlier in the week, two bombings in Iraq's capital left nearly two dozen pilgrims wounded.
The pilgrims are among tens of thousands of Shiites making their way to northern Baghdad's Kadhimiya Shrine. Many travel on foot. The pilgrimage is to commemorate the martyrdom of Imam Musa al-Kadhim, one of the 12 Imams of Shia Islam.
Iraqi authorities have stepped up security around the capital and routes leading to the shrine ahead of the weekend pilgrimage.
On Thursday, the Baghdad Operations Command announced a ban on motorcycles and pushcarts until Sunday.
This is the first pilgrimage to take place since U.S. combat forces completed their withdrawal from Iraqi cities and urban areas on June 30.
Iraqi authorities say they are securing this pilgrimage and have not used U.S. military support.
Maj. Gen. Qassim Atta, the spokesman for the Iraqi Military in Baghdad, said Friday that Iraqi forces planned and are executing the security plan on their own and are using their own air surveillance. Atta said the number of female searchers was increased this time.
Shiite pilgrims have been the target of bloody attacks in the past.
In April, two female suicide bombers struck near the Kadhimiya shrine, one of the holiest for Shiites, killing more than 65 pilgrims and wounding dozens.
CNN's Jomana Karadsheh contributed to this report.