(CNN) -- The World Health Organization said Saturday it is investigating a possible outbreak of polio in Syria, where an ongoing civil war has decimated the public health infrastructure.
The organization said it received reports Thursday of "a cluster of acute flaccid paralysis (AFP) cases" in the country. The cluster was detected early in the month in the eastern province of Deir Ezzor, it said.
"Initial results from the national polio laboratory in Damascus indicate that two of the cases could be positive for polio -- final results are awaited from the regional reference laboratory of the Eastern Mediterranean Region of WHO," it said.
Wild poliovirus -- which is highly infectious -- was last reported in Syria in 1999.
Syria's Ministry of Health "confirms that it is treating this event as a cluster of 'hot' AFP cases, pending final laboratory confirmation," and is planning an urgent, nationwide response, it said.
Neighboring countries were planning to increase their immunization activities, it added.
A worldwide eradication effort has been credited with helping reduce the incidence of the disease, which primarily affects children younger than 5, by more than 99% in the past quarter century, from 350,000 cases in 1988 to 223 reported cases last year, according to the WHO.
In 1988, the disease was endemic in more than 125 countries; this year, it is endemic in only three countries -- Afghanistan, Nigeria and Pakistan.
One in 200 infections results in irreversible paralysis. Of those who become paralyzed, 5% to 10% die when their breathing muscles are affected.
There is no cure for polio, but the vaccine -- given multiple times -- can protect for life.
Despite its precarious public health infrastructure, India succeeded in stopping polio in 2011.