The two images, which Stuff has chosen not to publish due to their graphic nature, show young children lying on the ground with wounds to their heads, torso and legs.
"What did these children do to deserve this?" Williams tweeted on Tuesday evening.
This summer share a thought for the innocent lives lost everyday in war."
Williams recently returned from visiting a refugee camp in Lebanon as a Unicef ambassador, working to bring awareness to the plight of Syrian children and their families living in the camps.
The All Blacks star said his time at the temporary settlements at Faida in the Bekaa Valley, east of Beirut and near the Syrian border, made him realise how little he knew about the refugee crisis.
"I came here and what I've heard, what I've seen, I've just been shocked and it's just made me realise how ignorant I was," he said.
"The thing that really touched me was, coming here, I didn't really know what a refugee was.
"I mean, I knew what a refugee was but did I really know? No, not until I came here. It kind of hit home, how ignorant I was."
Early responses to Williams' graphic tweet were mixed.
Some offered prayers and shared Williams' outrage.
"Oh my that just breaks my heart. Those poor babies. Their poor poor parents," tweeted one followers.
"The photos should be censored. Respecting the dead if Im not mistaken [sic]," tweeted one user.
"Although I sympathise [with your] reasons for posting this, it's not wise. It can be a trigger for some [people]. Also young followers," tweeted another.
Lebanon, which shares its eastern border with Syria, has given shelter to more than 1.2 million refugees since the Syrian conflict began five years ago.
Williams met with some of the children affected by the crisis who had been forced to flee their homes amid the violence.
He spent the majority of his day with a 12-year-old girl named Fatima, learning about her life at the camp and visiting her school at the settlement which is a temporary structure made from tents.
Fatima escaped to Lebanon from Syria with her family two years ago.
She had been left traumatised after seeing her best friend die in a bombing while they were walking together back in Syria.
Music has helped her overcome the horrific experience, and she has since created a support group with other girls in the community.
"We kind of clicked straight away," Williams said of the girl.
"Half-way through the day, she told me she loved having me here and she really opened up about a few of the stories she had encountered.
"It would shock me if a normal 12-year-old back in New Zealand or Australia would tell me these stories, but based on the situation that she's in, it didn't."
Fatima took Williams to visit the temporary structure she calls home, where she lives with her parents and four brothers.
The camp is set up on private property and the family told Williams they have to pay $US250 ($347) in rent each month for their land and tent where the kitchen doubles as the toilet.
Williams also spoke with Fatima's teenage brother, who labours long hours each day to earn money for the family as their father is too sick to work.
The experience left Williams, father to one-year-old daughter Imaan, feeling emotional.
"It's conditions you wouldn't want your worst enemy living in," he said.
But despite the family's circumstances, what surprised Williams most was the resilience the family showed.
"The amazing thing through all of this, I could relate to the similarities, how they are as human beings and how we are," he said.
"You can see how much the father and the mother love each other, and how much they love the kids and vice versa.
"You could see the kids just wanting to be kids, joking around, laughing, but you could see how much they miss their actual home."
Williams said hearing the stories and seeing the camp up close had shown him how out of touch the rest of the world was with a crisis that had forced more than two million people to become refugees.
"We're so lucky where we live, but we're so out of touch," he said. "Everyone's mindset is made to feel that refugees are a problem, but it's more than that.
"They're human beings too. They were forced from their homes.
"Everyone is fighting over who has to take them on, it's like everyone's reluctant to do that."
He hoped exposing the realities of life in a refugee camp with the following he has gained from his sporting success would help change the perceptions of refugees.
"I know no-one knows me over here, but there's a few people that know me in Australasia and I just thought, people are naturally good people.
"People have goodness in their hearts … Surely those people who see [the situation here] back home in Australia and New Zealand, it would change a few of their mindsets, how they see refugees."
Travelling with Williams was Unicef NZ executive director Vivian Maidaborn.
"Many of the girls are married off at age 12 because the fathers feel that being abused by one man is better than being abused by many," Maidaborn said.
"The young girls are married to old Lebanese men in their 30s. After a couple of years, some of the men divorce the young girls and abandon them."
But Maidaborn said equally upsetting was learning that many of the boys who fled Syria because of the violence and turmoil were now returning to join the army.
"With limited education and no work opportunities in Lebanon, young men have very limited options," she said.
"They see their fathers unable to work, frustrated and humiliated. They see their mums struggling with work, kids and the endless daily chores of water, cooking and firewood.
"They see their sisters married into abusive relationships when they are just young girls."
The boys who return and sign up to fight are paid US$500 ($728) a month, and send the money back to their family in the camps.
"They risk their lives in order to help their families get through the daily struggle of life in the settlements of Lebanon."