"The polio outbreak in Syria is not just a tragedy for children; it is an urgent alarm and a crucial opportunity to reach all under-immunised children wherever they are," Peter Crowley, who heads the UN children's agency's polio division, said in a statement.
The World Health Organisation last week confirmed the polio outbreak in Syria, which had been free of the disease since 1999.
"In a region that had not seen polio for nearly a decade, in the last 12 months polio virus has been detected in sewage samples from Egypt, Israel, the West Bank and Gaza Strip," WHO and UNICEF said in a joint statement.
"It has so far left 10 children paralysed, and poses a risk of paralysis to hundreds of thousands of children across the region," they stressed, pointing out that Syria has seen its immunisation rate plummet from more than 90 percent before the conflict began in March 2011 to 68 percent today.
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More than 650,000 children in Syria, including 116,000 in the strife-torn northeastern Deir Ezzor province where the polio outbreak was confirmed last week, had already received emergency vaccinations, UNICEF and the WHO said.
A new campaign aims to vaccinate 1.6 million children in Syria against polio, measles, mumps and rubella, while Jordan plans to immunise 3.5 million across the country, the UN agencies said, adding that some 18,800 kids had received vaccines in Jordan's Zaatari refugee camp in recent days.
Thanks to a global drive against polio, the virus is now endemic in just three countries: Afghanistan, Pakistan and Nigeria.
"Preliminary evidence indicates that the polio virus is of Pakistani origin and is similar to the strain detected in Egypt, Israel, the West Bank and Gaza Strip," Friday's statement said.