The King is "appalled" by and condemns the "barbaric acts" of terrorism in Israel," a Buckingham Palace spokesman has said.
The Palestinian militant group Hamas launched an unprecedented attack on Israel on 7 October.
Armed fighters crossed into Israel from Gaza, killing over 1,000 people and taking dozens of hostages.
At least 950 people have also been killed in the Gaza Strip by Israel's retaliatory airstrikes, according to the Gaza Health Ministry.
The 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.”
He added: “His Majesty is appalled by and condemns the barbaric acts of terrorism in Israel."
© GettyHELLO! understands that the King spoke to President Herzog of Isarel and to King Abdullah of Jordan on Wednesday afternoon and expressed his sadness and concern about the situation in the Middle East and his sympathy for those who have lost loved ones, as well as his hope for peace and ongoing commitment to interfaith dialogue.
Hamas has ruled the Gaza strip since 2007. The Gaza Strip is a 41km long and 10km-wide territory between Israel, Egypt and the Mediterranean Sea.
The current attack follows years of tensions between Hamas and Israeli governments.
On Monday, Britain's Prime Minister spoke at Finchley United Synagogue, saying: "I wanted to come here tonight to stand with you, to stand with you in this hour of grief as we mourn the victims of an utterly abhorrent act of terror, to stand with you in this hour of prayer, as we think of those held hostage and your friends and loved ones taking refuge in bomb shelters, or risking their lives on the frontline.
© Getty"And perhaps above all, I wanted to come here tonight to stand with you in solidarity in Israel's hour of need."
Mr Sunak also released a joint statement on Monday with the leaders of France, Germany, Italy, and the US after a call. The five countries make up the Quint international organisation.
It read: "We make clear that the terrorist actions of Hamas have no justification, no legitimacy, and must be universally condemned. There is never any justification for terrorism.
"In recent days, the world has watched in horror as Hamas terrorists massacred families in their homes, slaughtered over 200 young people enjoying a music festival, and kidnapped elderly women, children, and entire families, who are now being held as hostages.
© Getty"Our countries will support Israel in its efforts to defend itself and its people against such atrocities. We further emphasise that this is not a moment for any party hostile to Israel to exploit these attacks to seek advantage.
"All of us recognise the legitimate aspirations of the Palestinian people, and support equal measures of justice and freedom for Israelis and Palestinians alike. But make no mistake: Hamas does not represent those aspirations, and it offers nothing for the Palestinian people other than more terror and bloodshed.
"Over the coming days, we will remain united and coordinated, together as allies, and as common friends of Israel, to ensure Israel is able to defend itself, and to ultimately set the conditions for a peaceful and integrated Middle East region."
