By Doug Faulkner & Nick Beake
BBC News
More than 10 British citizens are feared dead or missing in Israel after the weekend's attack by Hamas, an official UK source has told the BBC.
Nathanel Young and Bernard Cowan are the only Britons confirmed to have died.
But the BBC understands photographer Dan Darlington is thought by his family to be dead.
More than 700 people have been killed in Israel since Hamas launched its attacks on Saturday morning.
That includes 260 at a music festival where Briton Jake Marlowe was providing security. He has been reported missing.
More than 500 people have been killed in Gaza after retaliatory Israeli air strikes.
More on Israel-Gaza attacks
Mr Cowan, from Glasgow, has also been identified by family members on social media as having been killed in the attack.
In a statement his family said: "We are grieving the loss of our son and brother, Bernard Cowan, who was horrifically murdered on Saturday during the surprise terrorist attack on Israel by Hamas.
"We ask for privacy at this time while we process this huge loss to our family, both at home and in Israel, and to the Jewish community in Glasgow where he will be sorely missed."
The north London school attended by Mr Young, who was 20 and serving with the Israel Defense Forces, is "devastated" by his death, its headteacher has said.
He went to the same school - North London's JFS Jewish School - as 26-year-old Mr Marlowe - who was reported missing from the Supernova music festival near Kibbutz Re'im, close to Gaza.
JFS headteacher Dr David Moody said: "We are heartbroken at what has happened.
"Nathanel is fondly remembered within the school and we think of him with nothing but love. Equally, we have seen reports that Jake Marlowe is missing and we all pray that he is found soon."
Mr Young's funeral, held at Israel's national cemetery Mount Herzl, was interrupted after loud bangs were heard over Jerusalem.
The authorities had asked that no more than 50 people attend the open-air service - so that, like other public gatherings, it could not be a target. In the end more than 1,000 turned out - and listened as Mr Young's brother Elliot pay tribute to him.
But when his sister started to remember him, an emergency siren pierced the tranquillity.
Mourners threw themselves to the ground, taking cover under trees and between gravestones.
Repeated explosions could be heard. Some began reciting prayers, others began to video-call loved ones.
After a few minutes, the alarm fell silent, and the funeral continued.
The UK government believes around 50,000 to 60,000 British nationals are in either Israel or Gaza.
It has said it is assisting the families of several individuals in Israel and in the Israeli-occupied West Bank and Gaza Strip but there are no plans for a UK-facilitated evacuation of British citizens.
The Israel embassy in London said: "We are receiving a lot of questions [about] the 10 British citizens. At the moment we don't have any information. We are working with British authorities."
The Foreign Office has advised against all but essential travel to the region due to the conflict.
Prime Minister Rishi Sunak said the UK government was working "very closely" with its Israeli counterparts to "establish the status of any British nationals on the ground".
He called the scenes from Israel "horrifying" and said "Hamas and the people who support Hamas are fully responsible for appalling acts of terrorism - call it out for what it is".
Following an emergency Cobra meeting Foreign Secretary James Cleverly refused to speculate about the number of Britons involved but said it was "unprecedented".
He said that due to Israel's "unique status" there were a large number of British-Israeli dual nationals - many of whom planned to stay in Israel or who were members of the Israel Defense Forces.
Consular numbers are available for those seeking to leave, he said, with flights still available if people wanted to do that.
Scotland's First minister Humza Yousaf has said his parents-in-law are "trapped" in Gaza.
He said the Israelis have told them to leave but they have no way to get out and the UK Foreign Office cannot guarantee safe passage.
Speaking at a vigil outside Downing Street, Chief Rabbi Ephraim Mirvis said he prayed that "the darkness we are enduring will lead to light. That the chaos, confusion and bitterness, the mourning and the grief, will be replaced by peace."
Israeli ambassador to the UK Tzipi Hotovely said it was "so clear that it is a fight between good and evil" and that "good will prevail".
A pro-Palestinian demonstration is taking place outside the Israeli embassy in west London, with hundreds gathered chanting slogans including "Free Palestine".
Large groups of police officers watched on as placards calling for Israel to "end the occupation" were waved.
Home Secretary Suella Braverman has written to police chiefs in England and Wales urging them to step up patrols and use their powers to prevent "disorder and distress to our communities".
She said: "There can be zero tolerance for anti-semitism. Sadly, we have seen in recent years how events in the Middle East are used as an excuse to stir up hatred against British Jewish communities.
"There is no place for demonstrations, convoys, or flag-waving on British streets that glorifies terrorism or harasses the Jewish community."
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