Iraqi police and US troops detained 400 people during search operations in two Shiite neighbourhoods of southwest Baghdad over the weekend and also seized weapons, the US military said on Saturday.
Police detained 400 people on Friday and seized four mines, an automatic weapon, ammunition and a host of other materials that could be used for making bombs and mines, the US military said in a statement.
"There was a large number of weapons confiscated," it said.
A spokesman for the Shiite radical movement of anti-US cleric Moqtada al-Sadr put the number of people held at more than 400.
The search operations lasted from 11 am to 2:30 pm in the neighbouring districts of Al-Amal and Al-Bayaa, a stronghold of Sadr's movement, the witnesses said.
"The Iraqi and US forces raided a mosque in Al-Amal as well as a neighbouring market and rounded up dozens of people, some of them elderly men or teenagers," Al-Amal resident Hazem Mohammed, 27, told AFP.
"My three brothers, one of whom's only 12, were picked up and so was my cousin," Mohammed said, adding that he had only narrowly escaped detention by the Iraqi troops himself.
Several other witnesses interviewed by AFP confirmed the scale of the round-up, carried out as the streets were busy with weekend shoppers.
A Sadr movement spokesman in Al-Amal, Hamadallah al-Rikabi, said: "Iraqi and US soldiers picked up more than 400 people... Including old men and even children."
He said the troops had no arrest warrants and he accused the soldiers of humiliating the detainees.