The King is “appalled” by and condemns the “barbaric acts” of terrorism in Israel, Buckingham Palace has said.
Charles is said to be “extremely concerned” about the situation and has asked to be actively updated in the wake of Hamas’ attacks.
A Palace spokesman said the monarch’s thoughts and prayers were with all of those suffering, especially those who had lost loved ones.
Israel has vowed unprecedented retaliation against the Palestinian militant group Hamas after its fighters stormed through the border fence on Saturday and shot hundreds of Israelis in their homes, on the streets and at an outdoor music festival.
The Israeli government has launched a major retaliation of air strikes on Gaza and stopped the passage of food, water, fuel and medicine into the territory.
The conflict has already claimed at least 2,100 lives on both sides, with fears it could escalate further.
A 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.”
He added: “His Majesty is appalled by and condemns the barbaric acts of terrorism in Israel.”
Charles, as the Prince of Wales, 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.
Her bravery was recognised by Israel which in 1993 posthumously bestowed the title of Righteous Among The Nations on her.
The princess – who was the mother of Philip, the late Duke of Edinburgh – is buried at the Church of St Mary Magdalene in Jerusalem.
The King’s son, then the Duke of Cambridge, toured Israel and the Occupied Palestinian Territories in 2018.
William met separately with both the then-Israeli president Reuven Rivlin and the Palestinian leader Mahmoud Abbas,.
He was urged by Mr Rivlin to take a “message of peace” to Mr Abbas to encourage him to take the “first step” to end the “tragedy” between their people.
