NAIROBI, Kenya (July 13, 2012)--The World Health Organization says it is concerned about an increasing number of cholera cases in a southern Somali town controlled by militants.

The WHO said Friday that the hospital in the port city of Kismayo has reported 639 suspected cases of cholera this year.

Cholera is a disease associated with diarrhea that can kill within hours if left untreated.

Most of its victims are children younger than 8.

Kismayo is the last major stronghold of militants from the group al-Shabab.

Kenyan military forces are slowly moving toward Kismayo and Kenyan leaders have vowed to take it from the militants by August.

WHO said it is sending in extra medical supplies, but said that limited access and recent fighting has made it difficult to respond fully to the outbreak.