All Black Sonny Bill Williams' tweet of two dead children at a Syrian refugee camp was done without Unicef's knowledge or approval, the children's charity says.

Photo: PHOTOSPORT

Williams, a United Nations Children's Fund ambassador, travelled to the camp in Lebanon's Bekaa Valley earlier this month to highlight the plight of the 1.2 million refugees fleeing the conflict in Syria.

The All Black tweeted, "what did these children do to deserve this", along with pictures showing the bodies of two young children with horrific injuries.

He asked people to spare a thought for "the innocent lives lost every day in war".

His action have drawn a mixed response from his Twitter followers, including one who asked him to spare a thought for his young followers. However, others applauded his actions.

If @SonnyBWilliams tweet made you feel uncomfortable and talk about Syria's most vulnerable, then good, that was the point. Well done SBW. — Mike McRoberts (@MrMikeMcRoberts) December 29, 2015

@SonnyBWilliams Ignorance is not knowing, thanks for being a voice for these defenceless precious children. #SBWforunicef — Keri Brown (@herapania) December 30, 2015

One follower responded "Sorry you feel the need to post pictures of dead bodies to highlight your cause", while another said the images were "tapu" [sacred].

Unicef executive director Vivien Maidaborn said Williams was not acting as an ambassador at the time.

"It was a personal act for him and I think it fits in the context of a person who is processing a war that has suddenly become very personal for him," she said.

"He has met children, he has touched them, he has been part of their families for some time."

Ms Maidaborn said Unicef would never post or publish such horrific images but did not condemn what Mr Williams did on a personal level, as it had achieved worldwide attention for the situation faced by children in the war-torn area.

"I would just see what he tried to do generously and come back to the core action, which is each of us asking the question 'what can we do to help the children of Syria'."