Yemen's health authorities have launched a polio vaccination campaign for more than 4 million children in the north of the war-torn country.
The three-day campaign launched on Saturday is supported by the World Health Organization, Unicef and other international aid agencies, Xinhua news agency quoted the authorities as saying.
The door-to-door immunization targets children under the age of five.
In August this year, a polio outbreak was declared in Yemen after 15 cases of vaccine derived poliovirus type 1 (cVDPV1) were reported.
The cases were detected in different districts of Sa'ada Governorate, in the north-west of the country.
Children aged from eight months to 13 years are affected.
Yemen has been mired in civil war since late 2014 when the Iran-backed Houthi group seized control of several northern provinces and forced the internationally-recognized government of President Abd-Rabbu Mansour out of the capital Sanaa.
The conflict has brought the impoverished Arab country to the brink of famine and triggered repeated outbreaks of deadly epidemics such as cholera and polio.
The UN is trying to resume peace talks between the government and the Houthi rebels to end more than five years of civil war.