Israel's military on Monday published new images and voiced concern about a mother and her two boys -- including a baby who is the youngest hostage seized by Hamas militants.
Hamas announced in November that all three had been killed in an Israeli bombardment but the Israeli authorities have not confirmed the claim.
Army spokesman Daniel Hagari said they were "concerned for the welfare" of Shiri Bibas, who was seen on a street camera in the southern Gaza city of Khan Yunis surrounded by seven armed men.
Kfir Bibas is the youngest Israeli hostage and was "stolen from his crib" in the community of Nir Oz when he was barely nine months old while his brother, Ariel, was just four, Hagari told a televised briefing.
If still alive, Kfir Bibas would have turned one year old on January 18.
In a statement on Monday, other members of the Bibas family described the images as "unbearable and inhumane" and called the kidnapping of children "a crime against humanity and a war crime".
"Ariel and Kfir are victims of monstrous evil. Our whole family has become hostages along with all the hostages," they added.
Prime Minister Benjamin Netanyahu vowed that "these kidnappers of babies and mothers" will be brought to justice.
Hamas has previously broadcast a video of the boys' father, Yarden Bibas, who was also seized in the October 7 attacks by Hamas militants which triggered the war with Israel.
Nir Oz in southern Israel was the scene of some of the bloodiest attacks on October 7, which led to the deaths of 1,160 people, most of them civilians, according to an AFP tally based on Israeli figures.
Israel vowed to "destroy" Hamas in response and has carried out a relentless bombardment and ground invasion that has killed more than 29,000 people, most of them women and children, according to the health ministry in Hamas-run Gaza.
More than 250 people were taken hostage, including more than 75 from Nir Oz. According to Israel, 130 hostages are still in Gaza but 30 are thought to be dead.
Images filmed by Hamas on October 7 of a terrified Shiri Bibas with her two children in her arms have become the defining images of the hostage crisis for Israelis.