A massive trade fair in Baghdad has been cancelled just days before it was to start, after the US State Department warned it could by targeted by rebels.
The State Department told US firms that "terrorists do not distinguish between official and civilian targets", a source close to the event told BBC News Online.
The cancellation follows the gruesome killing of four US civilians in Iraq.
The decision is a blow to US efforts to attract global investors to Iraq, as many were expected at the event.
The State Department also reportedly warned that the Baghdad Expo, scheduled to take place between 5 and 8 April, would have nearly coincided with the first anniversary of American forces' entry into Baghdad.
US soldiers stormed Baghdad and toppled a statue of fugitive Iraqi leader Saddam Hussein on 9 April 2003, after weeks of fighting.
With the anniversary looming, the US State Department warned that "it is not possible to guarantee security" for American citizens at the Baghdad event.
A number of private firms which had been tasked with securing the site were also reported to have voiced last-minute concerns about its vulnerability to insurgent attack.
The US government has spoken of its shock after four Americans working for a private security firm were shot dead and dismembered by a mob in the town of Falluja on Wednesday.
The Baghdad Expo was organised by the Iraqi-American Chamber of Commerce and Industry and was billed as the largest post-war gathering of businesses.
Bassam Qadoumi, whose firm was involved in sponsorship and transportation for the Expo, told BBC News Online many parties had invested a lot of money in the event.
He said he hoped it would be rescheduled.
The organisers have not said whether the event will now be held at a later date.
The Expo's website reveals a wide range of global corporations had planned exhibits.
The list includes Canon, DHL, General Electric, Daewoo, Samsung and Microsoft.
US firms already active in Iraq such as Bechtel and Halliburton were also planning a presence there.