ISTANBUL, Sept 17 (Reuters) - United Nations agencies said on Wednesday that a measles vaccination campaign in **rthern Syria had been halted after 15 children died following i**culations. "For as long as the facts remain unclear, the suspension of the immunization campaign in both Idlib and Deir Ezzour provinces is a wise step," the World Health Organisation and U.N. children's agency UNICEF said in a statement. (Reporting by Dasha Afanasieva)