UNITED NATIONS - A UN staff member has died as a result of the suicide bombing that struck the world body's offices in Abuja, the Nigerian capital, four months ago, the UN Children's Fund (UNICEF) confirmed on Wednesday.

Fred Simiyu Willis, an employee of the UNICEF, died on December 23 in South Africa, where he had been on medical evacuation after the blast, the UN agency said.

The Kenyan national had worked for the agency in Abuja since September 2004, serving as a health specialist focused on vaccine security, supply and logistics.

Willis'passing takes the UN death toll from the August 26 terrorist attack to 13, with 12 non-UN staff also killed.

Kate Donovan, a spokesperson for UNICEF, said the agency was deeply saddened by the death of Willis, whom she described as a " very dedicated" employee.

"It's a loss for the children of Nigeria and for all of us," she said, noting that Willis'efforts had helped to ensure immunization campaigns across the West African country.

"Our deepest condolences go out to his family and to his colleagues ... He was a very highly valued member of the staff," she added.