Meanwhile, Iraqi police said two vehicle bombs tore through Baghdad on Tuesday, killing at least 40 people and leaving scores wounded.
The deadly Memorial Day ambush by insurgents began, the U.S. military says, when an army helicopter started taking small-arms fire from insurgents north of Baghdad, just before evening, reports CBS News chief foreign correspondent Lara Logan.
The two-man crew on board were killed but not before radioing for help.
Six of the soldiers who answered the plea also lost their lives, hit by multiple roadside bombs as they rushed to the crash site, adds Logan. Five died in one Bradley armored vehicle, while the sixth soldier was killed trying to recover the damaged Bradley and its crew.
The deaths of the other two soldiers was made public later Tuesday, and it was not immediately clear where they died, or what caused the casualties.
It was not immediately known if the helicopter was shot down or suffered mechanical difficulties.
The number of American troops killed in Iraq in May now stands at 112.
The names of the soldiers killed Monday were being withheld until their families could be notified.
A parked minibus packed with explosives blew up Tuesday afternoon in a busy section of central Baghdad, killing 23 people and injuring 68 others, police said.
The attack in Tayaran Square occurred in an area filled with bus stops and shops, police said.
More than an hour later, a pickup truck parked in a market for spare car parts exploded in the Amil district in western Baghdad, killing 17 people and wounding 55, police said. The blast damaged 10 nearby houses and a Shiite mosque and set eight cars ablaze, police said.
Cars were riddled with shrapnel, pushcarts flipped upside down and smoke rose into the sky, witnesses said. Firefighters rushed to the scene and rescuers tried to pull the wounded out of cars, they said.
Also Tuesday, the British Foreign office confirmed that five Britons had been kidnapped during a raid at an office of the Iraqi Finance Ministry in Baghdad.
Earlier, the British Broadcasting Corporation reported that one analyst and four private security contractors had been nabbed in the raid.
An Iraqi government official told the Associated Press on Tuesday that three German citizens working for a German computer company were kidnapped.
All the missing Westerners were kidnapped by a group of gunmen who arrived at the ministry office — down the road from the main Finance Ministry building — in a long convoy of white sports utility vehicles, which are often used by police, the official said on condition of anonymity because he was not authorized to speak to the media.
Yousef Qasim, 37, was working in his clothing shop 200 yards away when the minibus blast tore through a line of buses waiting at the square, he said.
"I rushed there to see about four or five burning bodies," he said. "I saw flesh on the ground and pools of blood."
The blast comes a day after a suicide car bomber struck another busy commercial district in the capital, killing at least 21 people, setting vehicles on fire and damaging a nearby Sunni shrine, police and hospital officials said.
The Monday blast went off in the Sinak market area on the east side of the Tigris River
U.S. and Iranian officials met Monday in Baghdad under the auspices of Iraqi Prime Minister Nouri al-Maliki to try to end the violence in the war-torn country.
The United States ambassador in Baghdad said he and his Iranian counterpart agreed broadly on policy toward Iraq during four-houron Monday, but insisted that Iran end its support for militants.
Anti-American Shiite cleric Muqtada al-Sadr on Tuesday criticized the talks as interference in Iraq's internal affairs and warned Iraqi officials not to participate in them. "I call on the brave people to reject these negotiations," he said in a statement.
In other developments: