Foreign Secretary James Cleverly had said on Tuesday that a “significant number” of British-Israeli nationals had been caught up in the conflict.
Seventeen British nationals are feared dead or missing after the attack by Hamas over the weekend, as the conflict intensifies.
The BBC, citing an official source, said that 17 UK nationals are either dead or missing, including children.
A previous estimate had put the figure at more than 10.
Foreign Secretary James Cleverly had said on Tuesday that a “significant number” of British-Israeli nationals had been caught up in the conflict, which has already claimed at least 2,100 lives on both sides.
The UK Government has not confirmed any figures for those believed dead or missing, pointing to the fast-moving situation in the region.
Among those known to have died is Nathanel Young, 20, who was serving in the Israeli army when he was killed during Hamas’s charge.
Bernard Cowan, who grew up around Glasgow, also died.
Jack Marlowe, 26, who went to the same London school as Mr Young, is believed to be missing, while photographer Dan Darlington is feared dead.
A post from Mr Darlington’s sister Shelley on social media said he was “murdered” at Nir Oz, a kibbutz in southern Israel.
His death has not been officially confirmed.
Mr Marlowe was providing security at the Supernova music festival in the desert near Kibbutz Re’im when the area was set upon by Hamas gunmen.
It comes as the Israeli government continues to retaliate following the attack by Hamas, with air strikes targeted at locations across the Gaza Strip.
The UK and US governments have given a firm backing to Benjamin Netanyahu’s administration in the wake of the incursion by Palestinian militants.
But concerns have been expressed in the UN and elsewhere about the impact on civilians, as Israel embarks on a siege of Gaza in response to the attack.
Both Prime Minister Rishi Sunak and Home Secretary Suella Braverman have stressed the need to protect the UK’s Jewish community in recent days.
Ms Braverman told police chiefs on Tuesday that waving a Palestinian flag on British streets “may not be legitimate” if it is deemed to be a show of support for acts of terrorism.
Labour leader Sir Keir Starmer suggested that that flag-waving could be an issue in certain contexts.
“It’s very important that at times like this we don’t conflate peaceful discussion of Palestinian issues with Hamas.
“Now, the flags is a different situation. It really depends on the circumstances. If it’s provoking or encouraging attacks that might be one thing, there might be other situations.”
Sir Keir said that Israel had the right to defend itself, as he added his voice to calls for Wembley’s arch to be lit in the colours of the Israeli flag during the upcoming England friendly against Australia.
