Unicef says Sonny Bill Williams should not have tweeted photos of two dead Syrian refugee children.

The World Cup-winning All Black recently visited a refugee camp in Lebanon as a Unicef ambassador.

'What did these children do to deserve this?' Williams tweeted along with the graphic photos. 'This summer share a thought for the innocent lives lost everyday in war.'

Unicef NZ spokesman Patrick Rose said the posting of the images was entirely Williams's own choice and he did not consult with the charity before doing so. Unicef would not be sharing the images and asked its supporters to also refrain from doing so, Rose said.

'Unicef's mission is to protect the dignity and rights of children – even in death. Children have a right under a United Nations convention to how their image is portrayed and it is our joint responsibility to give children this right in death.'