The US military confirmed the twin crash, but did not give reasons why the helicopters came down on Saturday night. It was unclear whether they had been brought down by mechanical failure or ground fire from Iraqi fighters.
"The incident occurred at around 8.25pm (1725 GMT) in south-western Baghdad," US military spokesman Lieutenant Colonel Will Hutton said.
"The incident is under investigation."
US helicopters regularly come under attack from Iraqi fighters firing rifles and other weapons.
Meanwhile, the purported group allegedly led by Jordanian fugitive Abu Musab al-Zarqawi said it beheaded 11 members of the Iraqi police and national guard, a statement posted on a website said.
There has been no verification of
the website's decapitation claim
"Today alone, your brethren were able to decapitate 11 apostates affiliated to the so-called national guard and police force," said the statement of the military wing of the al-Tawhid wa al-Jihad group.
The statement did not give details, but a headline introducing it said the group had "killed 11 apostates" on Baghdad's Haifa Street, the site of frequent clashes between US forces and Iraqi armed fighters.
The authenticity of the statement has not yet been confirmed and the beheadings have not been independently verified.