All four hostages were kidnapped from kibbutzes near the Gaza Strip on 7 October.
In a statement via the Hostages and Missing Families Forum, relatives said news of the men’s deaths should “lead every leader to profound soul-searching”.
The statement added: “Chaim, Yoram, Amiram, and Nadav were kidnapped alive, some of them were with other hostages who returned in the previous deal – and they should have returned alive to their country and their families.”
UK Foreign Secretary David Cameron said in a post on X that he was “greatly saddened” to hear about Nadav Popplewell’s death. “My thoughts are with his loved ones at this terrible time for them,” he added.
Nadav Popplewell was kidnapped at his home along with his mother, who was eventually released. His brother Roy was killed in the attack.
Hamas killed about 1,200 people and took 251 others hostage during its attacks on southern Israel, according to Israeli authorities.
The group released 105 civilians during a week-long truce in November.
About 120 hostages remain unaccounted for. Israeli officials have said many are presumed dead.
Israel launched a military campaign to destroy Hamas in response to the cross-border attack.
At least 36,470 people have been killed in Gaza in almost eight months of fighting, according to the Hamas-run health ministry.
