Negotiations between Israel and Hamas to extend the Gaza truce were overshadowed at the last minute on Wednesday by an unconfirmed claim by Hamas that a family of Israeli hostages including a 10-month-old baby had been killed.

Shortly before the final release of women and children hostages scheduled under the truce, the military wing of Hamas said the youngest hostage, baby Kfir Bibas, had been killed in an earlier Israeli bombing, along with his four-year-old brother Ariel and their mother. Their father, who has also been held, was not mentioned in the statement.

Israeli officials said they were checking the Hamas claim, a highly emotive issue in Israel where the family is among the highest-profile civilian hostages yet to be freed.

“The IDF (Israel Defense Forces) is assessing the accuracy of the information,” the military said in a statement which said that it held Hamas responsible for the safety of all the hostages in Gaza.

Relatives had issued a special appeal for the family’s freedom after the children and their parents were excluded from the penultimate group freed on Tuesday.

An Israeli official said it would be impossible to extend the ceasefire, due to lapse on Thursday morning, without a commitment to release all women and children among the hostages. The official said Israel believed militants were still holding enough women and children to prolong the truce by 2-3 days. Egyptian security sources also said negotiators believed a two-day extension was possible.

Families of those Israeli hostages due to be released later on Wednesday had already been informed earlier of their names, the final group to be freed under the truce unless negotiators succeeded in extending it. Officials did not say at the time whether that included the Bibas family.

Gaza’s Hamas rulers published a list of 15 women and 15 teenage Palestinians to be released from Israeli jails in return for the hostages released on Wednesday. The hostages were seized by militants in their deadly raid on Israel on October 7.

For the first time since the truce began, the list of Palestinians to be freed included Palestinian citizens of Israel, as well as residents of occupied territory.

So far Gaza militants have freed 60 Israeli women and children from among 240 hostages, under the deal that secured the war’s first truce. Twenty-one foreigners, mainly Thai farmworkers, were also freed under separate parallel deals. In return, Israel has released 180 Palestinian security detainees, all women and teenagers.

The initial four-day truce was extended by 48 hours from Tuesday, and Israel says it would be willing to prolong it further for as long as Hamas frees 10 hostages a day. But with fewer women and children still in captivity, that could mean agreeing to terms governing the release of at least some Israeli men for the first time.