Peter Erben, in charge of the operation, told reporters in Amman on Sunday that some countries were concerned over the idea, but that the UN was working to address the issue.
"We are doing the best we can. When we will see that there is a country where we cannot work, we will refer this issue to the Iraqi government," the International Organisation for Migration (IOM) official said.
Up to one million Iraqi citizens living abroad were likely to want to participate in the 30 January elections, he said.
On Saturday, the IOM told the Iraqi electoral commission that it was having problems with Syria, Canada and Germany, which are concerned that polling centres might be attacked.
"We will be working very closely with the 14 countries to address the security issue and to provide a secure environment," Erben said.
The Switzerland-based OIM has been charged with organising the vote in 14 states: Australia, Britain, Canada, Denmark, France, Germany, Iran, Jordan, the Netherlands, Sweden, Syria, Turkey, United Arab Emirates and the United States.
Overseas voting will take place between January 28 and 30, with the use of indelible ink to avoid multiple voting. Iraqis living in other countries will be eligible to cast their ballots in any of the 14 states.
"We still have to determine which documentation will be acceptable," he said, adding that "the registration will take place over a seven-day period approximately two weeks before the election date."
The electoral commission had originally decided not to allow expatriate voting because of technical problems, but changed its mind in early November.
The IOM said Iraqi embassies would not be used for registration or voting as they do not exist in all earmarked countries.
Amman has been designated the main centre for the IOM to supervise the vote. Expatriates will only be allowed to vote in the 275-seat national assembly contest, and not for members of the 18 provincial councils.