The attack occurred at the entrance to the predominantly Shiite Muslim city, they added, about 100 kilometers (62 miles) south of Baghdad.
Two journalists employed by state-run Iraqiya TV died in the incident, CNN reported.
More than 700 Iraqis were killed, and nearly 1,400 injured, in terrorist attacks and sectarian violence in February, the United Nations said. It added nearly 8,000 were killed in 2013. Iraqi security forces have also been fighting al-Qaida insurgents along Iraq's western border with Syria.