Experts are concerned that polio may have made a return to war-torn Syria.
The World Health Organization says it has received reports of the first suspected outbreak in the country in 14 years.
Syrian's Ministry of Public Health is launching an urgent response, but experts fear the disease will be hard to control amid civil unrest.
Immunisation is almost impossible to carry out in regions under intense shellfire.
As a result, vaccination rates have been waning - from 95% in 2010 to an estimated 45% in 2013.
At least a third of the country's public hospitals are out of service, and in some areas, up to 70% of the health workforce has fled.
Outbreak risks have also increased due to overcrowding, poor sanitation and deterioration in water supply.
More than four million Syrians who have relocated to less volatile areas of the country are mostly living in overcrowded, unsanitary conditions.
The WHO says it is already seeing increased cases of measles, typhoid and hepatitis A in Syria.
Dr Jaouad Mahjour, director of the department for communicable diseases at WHO's regional office for the Eastern Mediterranean, said: "Given the scale of population movement both inside Syria and across borders, together with deteriorating environmental health conditions, outbreaks are inevitable."
The cluster of suspected polio cases was detected in early October 2013 in Deir al-Zour province.
Initial results from a laboratory in Damascus indicate that at least two of the cases could indeed be polio.
A surveillance alert has been issued for the region to actively search for additional potential cases. Supplementary immunisation activities in neighbouring countries are currently being planned.
WHO's International Travel and Health recommends that all travellers to and from polio-infected areas be fully vaccinated against polio.
Most people infected with the poliovirus have no signs of illness and are never aware they have been infected. These symptomless people carry the virus in their intestines and can "silently" spread the infection to thousands of others before the first case of polio paralysis emerges.
Polio is spread by eating food or drink contaminated with faeces or, more rarely, directly from person-to-person via saliva.