A helicopter belonging to a private U.S. security company was shot down over central Baghdad Tuesday, killing five civilians, a U.S. military official said.

A senior Iraqi military official who spoke on the condition of anonymity said the helicopter was brought down by machine gun fire Tuesday afternoon over the heavily Sunni Fadhil neighborhood in north-central Baghdad.

The Blackwater USA helicopter was responding to an attack on a private security detail on the ground and went down near Haifa Street.

On Friday, a U.S. Army Blackhawk helicopter was downed northeast of Baghdad and 12 service members were killed. A Pentagon official said there was evidence in the wreckage that it may have been shot down by a surface-to-air missile. U.S. military officials in Baghdad have not confirmed that and say an investigation into the crash was continuing.

Meanwhile, the U.S. military announced the deaths of three more U.S. troops, including a Marine who died Sunday from fighting south of Baghdad.

Two U.S. soldiers were killed Monday, the military said — one in fighting in the volatile Anbar province west of the capital and another in a roadside bombing.

Attacks targeting Shiites also persisted with bombs striking two separate areas in Baghdad on Tuesday, killing five people a day after a double car bombing tore through a market crowded with Shiites elsewhere in the capital in the bloodiest attack in two months.

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Witnesses reported clashes between gunmen and U.S. and Iraqi forces that lasted for several hours on Tuesday as helicopters flew low over the area. Police also said a car bomb struck a market in the district, killing at least three people and wounding 10.

U.S.-led forces also killed 16 suspected insurgents and detained 10 others Tuesday in the area surrounding Baghdad and Haditha, 140 miles northwest of the capital.

In Tuesday's violence, a parked car bomb exploded at 9 a.m. near the Finance Ministry, which is run by Bayan Jabr, a Shiite and former interior minister. One civilian was killed and four people were wounded, including a ministry guard, police said.

A bomb planted under a car exploded about 45 minutes later in the predominantly Shiite commercial district of Karradah in downtown Baghdad, killing four people, including a woman and a 7-year-old boy, and wounding seven other people, police said.

The blast collapsed part of the wall of a brick building, leaving a ground floor apartment exposed and a mass of rubble and mangled cars in the alley.

"Why are the insurgents detonating bombs near our houses every day? Everyday we have a blast, what have we done wrong? May Allah curse everybody who hurts the people," an unidentified elderly woman shrouded in black said as she stood amid the wreckage.

The attacks have battered Shiites during one of their holiest festivals and were the latest in a renewed campaign of Sunni insurgent violence before a U.S.-Iraqi push to secure Baghdad. The first of the 21,000 extra U.S. troops being sent to help quell the violence have started to arrive in Baghdad.

Insurgents also continued to target police in northern Iraq, with at least four officers killed during clashes throughout the northwest city of Mosul. Five insurgents also were killed and two detained in the fighting, police said.

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The Associated Press contributed to this report.