ERBIL, Iraq (Reuters) - A cholera outbreak in Iraq has spread to neighboring Syria, Kuwait and Bahrain, and risks turning into a region-wide epidemic as millions of pilgrims prepare to visit the country, UNICEF's Iraq director said.

The disease, which can lead to death by dehydration and kidney failure within hours if left untreated, was detected west of Baghdad in September and has since infected at least 2,200 people in Iraq and has killed six.

"It (the outbreak) already has a regional dynamic and the risk of that can only be increased by people from all over the region coming into Iraq," UNICEF country director, Peter Hawkins, said on Thursday. "Kuwait, Bahrain and Syria have already had confirmed cases."

Millions of Shi'ite Muslims are due to visit Iraq in December for Arbaeen, a religious ritual marking the end of an annual mourning period for the Prophet Mohammad's grandson Hussein, whose death in 680 AD entrenched the schism between Shi'ites and Sunnis.

Hawkins said UNICEF was working with clerics in the Shi'ite shrine cities of Najaf and Kerbala to convey information about how to guard against cholera, which is endemic in Iraq and the wider region.

The outbreak can be traced to a number of factors including low water levels in the Euphrates and winter flooding that has contaminated the river and shallow wells with sewage water.

The war against Islamic State militants who control large swathes of territory in northern and western Iraq has also contributed to the outbreak.

The conflict has displaced more than 3 million people, with many living in camps where conditions are conducive to the spread of cholera - a bite of contaminated food or a sip of contaminated water is enough to cause infection.

Hawkins said UNICEF has only limited access to areas controlled by Islamic State, which swept across the Syrian border in mid-2014 in a bid to establish a modern caliphate.

Higher military expenditure and other costs associated with the battle against Islamist militancy has aggravated a cash crunch for Iraq, a major OPEC oil producer that has suffered from the drop in global crude prices over the past year.

A higher proportion of the government budget is also being spent on security at the expense of other services and infrastructure such as water supply, Hawkins said.

One in five of the confirmed cases in Iraq is among children, and in large parts of the country the start of the school year was delayed by a month as a precaution, UNICEF said in a statement.

In response to the outbreak, UNICEF is providing bottled water, oral rehydration salts and installing community water tanks, but like most humanitarian operations in Iraq it is severely underfunded.

(Editing by Louise Ireland)