The Hostages Families Forum commented on the announcement that the body of hostage Hamza al-Ziyadne was identified.
"Our hearts break once again upon receiving news of Hamza al-Ziyadne's murder in Hamas captivity. The lengthy identification process is painful evidence of the urgency needed in returning the deceased for burial," the forum stated.
It added: "Four family members were kidnapped, with only two returning alive. Youssef and Hamzah, who survived a period in the hell of Gaza captivity, could have been saved through an earlier agreement.
"The time and conditions are ripe for all the hostages to return - bringing the living home for rehabilitation and the deceased for proper burial. The negotiations must be expedited to secure an immediate deal for their return. This historic window of opportunity stands before us and must not be lost."