Cholera has crossed the border in the Middle East from Iraq to Iran, further revealing the need for neighbouring countries to boost their defences against the deadly disease, the World Health Organisation (WHO) has said.

Cholera has struck at least 3,315 people in Iraq since mid-August, killing at least 15. WHO global cholera coordinator Claire-Lise Chaignat said that up to 10 cases have also been confirmed in Iran, near the Iraqi border.

It was not clear whether these were Iraqi refugees or local Iranians, according to the Swiss expert, who warned the epidemic could threaten refugee camps in the region if not controlled.

"Some cases, around nine or 10, have been confirmed in Iran. The situation seems contained," in the Islamic Republic, Chaignat told Reuters in Geneva.

Cholera, which is continuing to spread within Iraq, can be carried by refugees and pilgrims, and through normal trade, she said. "Borders are permeable, closing them won't stop the germ."

The virulent disease is characterised by a sudden onset of acute watery diarrhoea that in severe cases can cause death by dehydration and kidney failure within hours. It is transmitted mainly through contaminated water and food.

Iraq shares borders with Iran, Turkey, Syria, Jordan, Kuwait and Saudi Arabia. Some 60,000 Iraqis flee their homes each month and 2.2 million Iraqis have crossed into neighbouring countries, mainly Syria and Jordan, according to the United Nations.

"We are particularly worried about countries with Iraqi refugees where they don't always have access to good water and sanitation and hygienic conditions," Chaignat said. "It is important to catch the first cases and treat them correctly."

Countries should stock up on intravenous fluids and oral rehydration salts to combat dehydration in victims, she said.

The U.N. agency said it did not recommend any travel or trade restrictions on Iraq. "However, neighbouring countries are encouraged to reinforce their active surveillance and preparedness systems," it said in a statement.

The majority of cases have been in northern Iraq, with some 2,300 reported in Kirkuk and 870 in Sulaimaniya. Iraq's Health Ministry said on Monday that 15 people had died of cholera to date.

Chaignat said cholera normally thrives in lower temperatures and warned it could spread further in Iraq as the strong sun and heat which kill the germ subside. "That is our fear," she said.

The number of cholera deaths has "remained low throughout the outbreak indicating that those who have become sick have been able to access adequate treatment on time", the WHO said.

The overall quality of water and sanitation in Iraq is "very poor", which greatly facilitates cholera contamination.