Updated

Four of the five Americans killed when a U.S. security company's helicopter crashed in a dangerous Sunni neighborhood in central Baghdad were shot execution-style in the back the head, Iraqi and U.S. officials said Wednesday.

A senior Iraqi military official also said the helicopter had been shot down, but this was disputed by a U.S. military official in Washington.

The Iraqi said the helicopter was hit by a machine gunner over the Fadhil neighborhood on the east side of the Tigris River, while the U.S. official said initial reports gave no indication that the aircraft, owned by Blackwater USA, had been shot down. The Americans said they did not know what caused the aircraft to crash.

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In Washington, a U.S. defense official said the four had been shot in the back of the head but it was unclear whether they were alive or already dead or dying when they were shot.

It also was not clear whether the small aircraft was shot down in the common sense — that is, whether gunfire actually brought it down or caused the craft to drop toward the ground, where it got caught in electrical wires, he said on condition of anonymity because he was not authorized to speak on the record.

The helicopter was virtually destroyed and after investigating the site, U.S. forces had been planning to blow it up to keep people from scavenging the parts but the official didn't know whether that had been done.

The Iraqi official, who also declined to be identified because details had not been made public, said the four were shot in the back of the head while they were on the ground but did not elaborate.

Violence was unrelenting in Iraq on Wednesday with nearly 20 people killed or found dead, including four policemen who died when a parked car bomb exploded as their patrol passed in western Baghdad.

U.S. and Iraqi troops also clashed with gunmen in a Sunni insurgent stronghold north of the heavily fortified Green Zone on Wednesday, leaving as many as 30 insurgents killed and 27 captured, according to Iraqi officials.

The ministry added that the forces seized weapons that were hidden at a local school in Haifa Street on the west bank of the Tigris River.

Black smoke rose from the area, about two kilometers (about a mile) north of the Green Zone, site of the U.S. and British embassies as well as the Iraqi government headquarters. Apache attack helicopters buzzed overhead.

Iraq's Defense Minister Mohammed al-Askari said 30 insurgents were killed and 27 arrested, including four Egyptians and a Sudanese man.

The U.S. military said Iraqi army and American soldiers had launched targeted raids to clear the area of militants in an operation dubbed Tomahawk Strike 11 but faced fierce resistance from insurgents wielding hand-held grenades, rocket-propelled grenades and small arms fire from high-rise buildings in the area.

It said seven suspected insurgents were detained and heavy weapons were seized, including numerous rocket-propelled grenades, anti-tank rounds and 155 mm artillery rounds.

At least one civilian was killed and seven others were wounded due to the clashes, which began on a smaller scale on Tuesday, according to hospital and police officials.

The clashes broke out as U.S. and Iraqi troops gear up for a broader security crackdown to quell the sectarian violence in the capital. Al-Askari said the fighting on Wednesday was not part of that plan.

Haifa Street, a major avenue in central Baghdad, was built in the late 1970s and former leader Saddam Hussein had several concrete high-rises built for loyalists.

It has been the site of numerous clashes, including a major battle on Jan. 9, just three days after Prime Minister Nouri al-Maliki announced his new security plan for pacifying Baghdad.

Blackwater USA confirmed that five Americans employed by the North Carolina-based company as security professionals were killed. The statement from spokeswoman Anne Tyrrell did not provide identities or any details of the fighting.

Another American official in Baghdad, who spoke on condition of anonymity, said three Blackwater helicopters were involved. One had landed for an unknown reason and one of the Blackwater employees was shot at that point, he said. That helicopter apparently was able to take off but a second one then crashed in the same area, he added without explaining the involvement of the third helicopter.

That account would help explain why only four of the men were reportedly shot execution-style.

The New York Times, citing unnamed American officials, reported that the helicopter's four-man crew was killed along with a gunner on a second Blackwater helicopter.

The Qatar-based Al-Jazeera television said the 1920 Revolution Brigades insurgent group claimed responsibility for shooting down the helicopter and showed a video taken by a cell phone of a mass of still-smoldering twisted metal that it was said was the wreckage of the chopper.

Another Sunni insurgent group, the Ansar al-Sunnah Army, also claimed responsibility for the same attack and posted identity cards of men who were on the helicopter on a Web site, including at least two that bore the name of Arthur Laguna, who was later identified by his mother as among those killed.

Laguna was a 52-year-old pilot for Blackwater who previously served in the Army and the California National Guard, his mother, Lydia Laguna, of Rio Linda, Calif., told the AP in a telephone interview Tuesday night. She said she received a call from her other son, also a Blackwater pilot in Baghdad, notifying her of Arthur's death.

U.S. Ambassador Zalmay Khalilzad offered condolences for the five Americans killed, calling them good men and saying he had traveled with them.

"We had a very bad day yesterday," Khalilzad told reporters during a roundtable discussion at the embassy in the heavily fortified Green Zone in Baghdad. He did not give more details, saying it was difficult to know exactly what happened because of "the fog of war."

Witnesses in the Fadhil neighborhood told the AP that they saw the helicopter go down after gunmen on the ground opened fire, possibly striking the pilot or co-pilot or both. Accounts varied, but all were consistent that at least one person operating the aircraft had been shot and badly hurt before the crash.

The helicopter was believed to have been flying escort above a VIP convoy on the ground as it headed away from the heavily fortified Green Zone to an undisclosed destination.

A report in the Washington Post, also citing unnamed U.S. officials, said one of the Blackwater victims was killed as he traveled with the convoy on the ground.

Blackwater USA provides security for State Department officials in Iraq, trains military units from around the world, and works for corporate clients.

"These untimely deaths are a reminder of the extraordinary circumstances under which our professionals voluntarily serve to bring freedom and democracy to the Iraqi people," the Blackwater statement said.

Before Tuesday's crash, at least 22 employees of Blackwater Security Consulting or Blackwater USA had died in Iraq as a result of war-related violence, according to the Web site iCasualties.org, which tracks foreign troop fatalities in Iraq. Of those, 20 were Americans, and two were Polish.

The crash of the small surveillance helicopter, believed to be a version of the Hughes Defender that was developed during the Vietnam War, was the second associated with the U.S. war effort in Iraq in four days.

A U.S. Army Blackhawk helicopter went down Saturday northeast of Baghdad, killing all 12 service members on board. The American military in Baghdad has refused to confirm a report by a Pentagon official that debris at the crash site indicated the helicopter was shot out of the air by a surface-to-air missile.

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