"We're in contact with Israeli authorities, and British nationals in Israel should follow travel advice."
A White House National Security spokesperson said the US "unequivocally condemns" the attacks and stands with Israel, broadcaster CNN reported.
French president Emanuel Macron said he "strongly condemns the terrorist attacks that are currently striking Israel".
"I express my full solidarity with the victims, their families and their loved ones," he said.
Smoke rises over Gaza City on October 7, 2023 during Israeli air strikes (Photo: Getty)
EU Commission chief Ursula von der Leyen said: "I unequivocally condemn the attack carried out by Hamas terrorists against Israel. It is terrorism in its most despicable form."
Ukrainian President Volodymyr Zelensky, whose country is fending off a Russian invasion, said Israel had an unquestionable right to defend itself from attacks from Hamas terrorists.
"Israel's right to defence is indisputable," Zelensky said on Telegram.
"Terror is always a crime, not just against one country or specific victims, but against humanity as a whole," he added.
"The world must stand united... so that terror does not attempt to take or destroy life anywhere and at any moment.”
German chancellor Olaf Scholz posted on social media: "Terrifying news reaches us today from Israel.
“We are deeply shocked by the rocket fire from Gaza and the escalating violence. Germany condemns these attacks by Hamas and stands by Israel.”
Turkish President Recep Tayyip Erdogan called on Israelis and Palestinians to act with restraint and refrain from hostile acts that could exacerbate the situation.
"We call for restraint from all parties," Erdogan said at a congress for his ruling AK Party in Ankara. "They must refrain from aggressive acts," he said.
Israeli security forces on road 232 near the southern Israeli city of Sderot (Photo: Flash 90)
Egypt, historically a key mediator in conflicts between the two sides, warned of the "dire danger of ongoing escalation".
The Egyptian foreign ministry in a statement appealed to "both the Palestinian and Israeli sides to exercise the highest degrees of restraint".
Israeli president Isaac Herzog called for the international community to unite in its condemnation of Hamas.
Herzog said in a statement: “Today we saw the true face of Hamas. A terrorist army whose only goal is the cold-blooded murder of innocent men, women, and children.
“Supported and directed by their proxy commanders in Iran, they carried out an unprovoked, heinous attack against the Jewish state on a Jewish holy day. Innocent civilians were massacred and wounded, and many are still under attack.”
He added: “The State of Israel will take all measures necessary to eliminate this clear and immediate danger to our citizens. Israel will overcome in the face of all challenges.
“I call upon the family of nations – this war waged against us marks a line in the sand. Now is the time to hear clear, unequivocal condemnation of Hamas, its allies, and its backers in Iran. Now is the time to stand firm with Israel in support of its just and moral battle in the face of an abhorrent enemy."
Meanwhile, an adviser to Iran's Supreme Leader Ali Khamenei congratulated the Hamas fighters, the semi-official ISNA news site reported.
"We will stand by the Palestinian fighters until the liberation of Palestine and Jerusalem," it quoted Yahya Rahim Safavi as saying.
Iran's state television showed parliament members rising from their seats to chant "Death to Israel".
