Only 290 cases have been confirmed in laboratory tests, but WHO spokeswoman Fadela Chaib said the agency considered all cases of acute watery diarrhoea should be considered as carrying the "vibrio cholerae" bacteria.
At the end of August, authorities in Sulaimaniyah had reported 2,000 suspected cases and six deaths, while the WHO said another source was found in Kirkuk.
Chaib said Tuesday that six laboratory confirmed cases were also reported in Erbil.
"It is unclear what is the cause of the epidemic," Chaib told journalists.
"There is some evidence in Sulaimaniyah... that polluted water on which the local people were forced to rely on may have been to blame, and in Kirkuk a cracked water pipe."
"We are confident that it can be contained," she told journalists.
The WHO has sent two truckloads of antibiotics to the region, while the Iraqi government and provincial authorities have also taken measures to combat the disease.
The agency is not recommending any special travel or trade restrictions for the affected area, it said in a statement.
Previous cholera outbreaks hit northern Iraq in 1999 and southern areas around Basra shortly after the US-led invasion in 2003.