The Foreign Office is investigating a claim by Hamas that a British-Israeli hostage has died in Gaza.
Hamas, proscribed as a terrorist group by the UK government, claims Nadav Popplewell died of wounds sustained in an Israeli airstrike more than a month ago.
Mr Popplewell, 51, was seized with his mother Channah Peri on 7 October when fighters crossed the border fence and launched deadly attacks in Israel.
The Israeli military is yet to comment.
A Foreign Office spokesperson said it was urgently seeking more information on the matter.
It added that the department's thoughts "are with his family at this extremely distressing time."
In a brief statement via the Hostages and Missing Families Forum, the family of Mr Popplewell asked media organisations not to publish footage of him released by Hamas on Saturday, which shows him in captivity with a black eye.
Mr Popplewell's sister Ayelet Svatitzky told the BBC last October how gunmen had attacked the kibbutz in southern Israel where they lived, killing her older brother Roi.
On the day of the attack, Ms Svatitzky said she received two pictures, sent by the attackers from her mother's phone, showing the pair sitting in her mother's living room. Underneath was written "Hamas" in English.
Hours later, a third picture was posted on her mother's Facebook showing them with an armed Hamas gunman in the corner.
Ms Svatitzky's mother was released last November during a temporary ceasefire agreed between Hamas and Israel.
Israel says 128 hostages are unaccounted for.
