BAGHDAD, Iraq (CNN) -- The Iraqi Interior Ministry estimates that about 1,000 people have been killed throughout Iraq in the past week due to gunbattles, drive-by shootings and bomb attacks, a ministry official said Sunday.

The figure includes members of militia and terrorist groups, civilians and Iraqi security forces. The official said the data was gathered by Iraq's Interior, Health and Defense ministries.

The grim estimate came just a day after a bloody bomb attack on a crowded market in central Baghdad that killed 128 people and wounded 343 others Saturday, according to a Health Ministry official.

The incident, which also destroyed cars and surrounding stores, occurred in Sedriya, a mixed district of Sunni Arabs, Shiites and Kurds.

The Health Ministry official said he expected the death toll from that attack to rise. Already, it is the deadliest attack in Iraq since November 23, when Shiites were targeted by coordinated car bomb attacks in Sadr City. At least 200 civilians were killed in those attacks.

Jihad Jabri, head of the Interior Ministry's bomb squad, said a Mercedes truck used in Saturday's blast contained a ton of explosives.

Iraqi Prime Minister Nuri al-Maliki blamed the attack on Saddam Hussein loyalists and Sunni extremists. a

18 killed in Sunday attacks across Iraq

Four people were killed and 20 wounded Sunday when a car bomb exploded near a bus station in the town of Khalis, about 12 miles (20 kilometers) north of Baquba, an official with Baquba police told CNN.

In Kanan, about 12 miles east of Baquba, five people were wounded when a motorcycle rigged with explosives detonated near an outdoor market, police said.

Baquba is about 37 miles (60 kilometers) north of Baghdad.

In Baghdad on Sunday, gunmen, bombs and mortar attacks killed 14 people and injured 46 more, Baghdad police officials said.

The deadliest attack was a roadside bomb that exploded near an Iraqi police patrol in the northern Baghdad neighborhood of Kasra, killing four Iraqi police officers.

Other victims were killed or wounded by roadside and car bombs, attacks on their vehicles by gunmen, and mortar fire on a residential neighborhood, police said.

Iraqiya TV anchor Suhad Ibrahim was wounded when U.S. forces opened fire on her car while she was driving behind a U.S. military convoy near the Iraqi Foreign Ministry, Baghdad police said. The U.S. military did not immediately comment on the incident.

U.S.: Ground fire apparently brought down four helicopters

An ongoing U.S. military investigation has found that ground fire apparently brought down four U.S. helicopters in Iraq over the past few weeks, a Multi-National forces spokesman said Sunday.

The crashes killed 21 Americans.

"It does appear that they were all the result of some kind of Iraqi ground fire that did bring those helicopters down," U.S. Maj. Gen. William Caldwell said.

The downed helicopters -- which include two Apaches, a Black Hawk and a U.S. security contractor's helicopter -- pose a concern for the coalition in Iraq, where aircraft play a critical role. It could signal growing sophistication among insurgents determined to shoot down coalition aircraft.

Caldwell said the military is already making adjustments in tactics, techniques and procedures.

On Friday, chairman of the Joint Chiefs of Staff Gen. Peter Pace said that ground fire has been "more effective against our helicopters" in recent weeks and the military is studying the development.

The most recent crash occurred Friday when an AH-64 Apache flying northwest of Baghdad near Taji was shot down. Two U.S. soldiers were killed.

The next day, an al Qaeda-linked group claimed responsibility for the downed helicopter, claiming that God has granted them "new ways" to confront aircraft.

Earlier downings of aircraft believed to be the result of hostile ground fire include a U.S. military helicopter that went down January 29 during a battle in Najaf, killing two soldiers aboard; a U.S. helicopter that crashed in eastern Baghdad January 23, killing five employees for the Blackwater private security company; and a Black Hawk helicopter that went down in Diyala province on January 20, killing 12 U.S. troops.

Other developments

• One man suspected of leading a car bomb cell was killed and five suspected cell members were arrested Sunday in Mosul by U.S. forces, the military announced. Coalition forces also detained two suspected terrorists during a raid in Baghdad, the military said.
• In Kirkuk, north of the capital, the casualty toll from a series of nine bomb attacks launched Saturday rose to three dead and 23 wounded, Iraqi police told CNN on Sunday. Seven of the bombs were car bombs and the other two were roadside bombs, occurring in different locations across the city. A suicide car bombing at the headquarters of the Kurdistan Democratic Party was among the attacks.

CNN's Mohammed Tawfeeq and Barbara Starr contributed to this report.

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