Israel ordered its state-run electricity company to halt supply to the Gaza Strip on Saturday after Palestinian militant group Hamas launched a surprise attack on Israel, the energy minister said.
"I have signed an order instructing (Israel) Electric Company to stop the electricity supply to Gaza," AFP quoted Energy Minister Israel Katz saying in a statement.
Also, the Israeli prime minister's office said the security cabinet had approved steps to destroy the military and governmental capabilities of Hamas and Islamic Jihad "for many years", including cutting electricity and fuel supplies and the entry of goods into Gaza.
At the White House, President Joe Biden went on national television to say Israel had the right to defend itself and issued a blunt warning to Iran and other countries hostile to Israel. "This is not a moment for any party hostile to Israel to exploit these attacks to seek advantage. The world is watching," he said.
A senior Biden administration official told reporters that the United States was working with other governments to make sure the crisis does not spread and is contained to Gaza.
Long after nightfall, residents had not been given the all-clear to go home.
"It's not over because the (army) hasn’t said the kibbutz is clear of terrorists," Dani Rahamim told Reuters by telephone from a shelter where he was hiding in Nahal Oz, close to the Gaza fence. Gunfire had subsided but regular explosions could still be heard.
Hamas deputy chief Saleh al-Arouri said the group was holding a large number of Israeli captives, including senior officials. He said Hamas had enough captives to make Israel free all Palestinians in its jails.
Hamas, which advocates Israel's destruction, said the attack was driven by what it said were Israel's escalated attacks on Palestinians in the West Bank, Jerusalem and against Palestinians in Israeli prisons.
"This is the day of the greatest battle to end the last occupation on earth," Hamas military commander Mohammad Deif said, announcing the start of the operation in a broadcast on Hamas media and calling on Palestinians everywhere to fight.
Gaza has been devastated by four wars and countless skirmishes between Hamas and Israel since the militants seized control of the strip in 2007. But the scenes of violence inside Israel itself exceeded anything there even at the height of the Palestinian Intifada uprisings of past decades.
That Israel was caught completely off guard was lamented as one of the worst intelligence failures in its history, a shock to a nation that boasts of its intensive infiltration and monitoring of militants.
Scores of Palestinians were killed and hundreds wounded in clashes at Gaza's border into Israel, where fighters captured the crossing point and tore down fences. Some of the dead were civilians, among crowds that attempted to cross into Israel through the damaged gates.