The Prince and Princess of Wales “utterly condemn” Hamas’s attack on Israel, a spokesperson said.
The King and other senior royals have condemned the attacks by the militant group Hamas on Israel.
Palace sources said the King was “appalled”, and condemns the “barbaric acts of terrorism in Israel”.
The Prince and Princess of Wales are “profoundly distressed” by the events since strikes began on Saturday, according to their spokesman.
He said the couple believe all Israelis and Palestinians will be “stalked by grief, fear and anger”.
The King has asked to be kept updated on the situation and his “thoughts and prayers are with all of those suffering”, a palace spokesman said earlier.
Some 1,200 people have been killed in Israel, while more than 1,000 have died in retaliatory air strikes on Gaza.
The Buckingham Palace spokesman said: “This is a situation His Majesty is extremely concerned about, and he has asked to be kept actively updated.
“His thoughts and prayers are with all of those suffering, particularly those who have lost loved ones, but also those actively involved as we speak.”
Prince William and Catherine, meanwhile, said they hold “all the victims, their families and their friends in their hearts and minds”, according to a spokesperson.
“The horrors inflicted by Hamas’s terrorist attack upon Israel are appalling; they utterly condemn them.”
“Those the Prince of Wales met in 2018 overwhelmingly shared a common hope – that of a better future.”
“The prince and princess continue to share that hope without reservation”.
At least 17 British nationals, including children, are dead or missing after the Hamas attack on Israel, an official UK source has told the BBC.
Palestinian militant group Hamas launched a series of unprecedented attacks on Israel from Gaza over the weekend, killing hundreds and taking up to 150 people hostage.
In response, Israel has launched air strikes on Gaza and prevented the passage of food, water, fuel and medicine into the territory.
More on Israel Gaza war
Palace sources also said this afternoon that the King has spoken by phone to President Isaac Herzog of Israel and King Abdullah II of Jordan.
They said he has a deep concern about the situation in the Middle East, and used the opportunity to express his thoughts and prayers for all of those suffering, especially to the loved ones of those who have lost their lives.
Elsewhere, the Archbishop of Canterbury has also condemned the “utterly abhorrent” attacks by Hamas.
In a letter to the Board of Deputies of British Jews, Justin Welby said such violence against innocent civilians including children and the elderly “strikes at the heart of all that is good and holy”.
He added that British Jews would also be feeling the “double jeopardy” of anticipating an increase in antisemitic sentiment.
Meanwhile, Foreign Secretary James Cleverly has travelled to Israel, with the Foreign Office saying the visit was to meet survivors and outline the UK’s support for Israel.
A Foreign Office spokesperson said Mr Cleverly was in Israel “to demonstrate the UK’s unwavering solidarity with the Israeli people following Hamas’ terrorist attacks”.
British nationals Nathanel Young, Bernard Cowan and Jake Marlowe are confirmed to have died in the attacks, while the family of photographer Daniel Darlington believe him to be dead.
