Israel's President Isaac Herzog thanked the King for his support and said his words were an "important statement" which would serve as a "great comfort to the people of Israel".

Mr Herzog's office said in a statement: "President Isaac Herzog spoke today with the King of the United Kingdom, King Charles III, who called to express his condolences and deep shock at the criminal and barbaric actions of the terrorist organisation Hamas in its attack on the citizens of Israel."

The statement added: "The two talked at length about the terrible massacre and how it was carried out.

"The conversation between the two took place as part of a series of conversations the president has been holding on a daily basis with leaders from all over the world, including leaders of international organizations, and Jewish community leaders."

The King has also asked to be "actively updated" on the conflict as he is "appalled" by the "barbaric acts of terrorism" in Israel, Buckingham Palace has said.

The spokesman said the King is "extremely concerned" and his "thoughts and prayers are with all of those suffering".

Meanwhile, in a statement on X, formerly known as Twitter, a spokesperson for the Prince and Princess of Wales said: "[They] are profoundly distressed by the devastating events that have unfolded in the past days.

"The horrors inflicted by Hamas's terrorist attack upon Israel are appalling, they utterly condemn them.

"As Israel exercises its right to self defence, all Israelis and Palestinians will be continued to be stalked by grief, fear and anger in the time to come."

Key developments in the conflict:
• Met Police appeals for people to send them footage of attacks in Israel
• 17 British nationals, including children, killed or missing, Sky News understands
• Netanyahu and opposition agree to form emergency government
• At least 1,200 Israelis dead and more than 2,700 injured, IDF says
• At least 1,100 Palestinians dead and 5,184 injured in Israeli strikes, Gaza Health Ministry says
• Hamas attacks airport shortly after BA flight was due to land
• Sky correspondent visits kibbutz that became site of a massacre

The royals have issued statements as British Foreign Secretary James Cleverly is in Israel to express the UK's "solidarity" in the wake of the Hamas attacks.

Mr Cleverly was seen running for cover as air sirens blared in the city of Ofakim.

He later said in a statement on X: "Today I've seen a glimpse of what millions experience every day.

"The threat of Hamas rockets lingers over every Israeli man, woman and child.

"This is why we are standing shoulder to shoulder with Israel."

The Israeli foreign ministry said the siren was warning citizens of incoming Hamas rocket fire.

The King's connection with Israel

When he was the Prince of Wales, the King carried out his first official tour of Israel and the Occupied Palestinian Territories in 2020.

It marked the highest-level visit by a member of the monarchy to Israel and the Palestinian areas.

He visited the grave of his grandmother Princess Alice, who was famed for offering refuge to Jewish people during the Second World War in Nazi-occupied Athens.

Gaza runs out of power as violence continues

Israel is continuing its bombardment of Gaza in response to a surprise attack on the country by Hamas over the weekend.

Israel is carrying out a "total siege" of Gaza to stop the entry of food, fuel and medicines into the territory.

The city of 2.3 million people has been left without electricity after its sole power station ran out of energy.