Israeli defence minister Yoav Gallant said Israel was "battling beastly people" and was conducting itself as such, after Hamas launched a surprise attack from Gaza on Sunday.

The Israeli infrastructure minister Israel Katz said he had ordered the water supply between Israel and Gaza to be shut off immediately.

It comes as a "huge rocket barrage" out of Gaza hit central Israel late on Monday morning.

More than 1,000 Palestinian targets hit - follow live updates

Israeli forces are currently fighting Hamas in two locations inside Israel, after the country formally declared war on the militant group.

Around 300,000 reservists have been called up by the Israeli military.

Doron Spielman, a spokesperson for the Israel Defence Forces (IDF), said, there is still active fighting with Hamas militants "constantly trying to cross over" the border from Gaza.

This is despite Israeli troops having regained control in some areas of southern Israel.

"They keep stringing to the border and we expect this to continue because there's a massive number of jihadis that have been trained to do this," he told NBC.

Other key developments include:
• More than 1,200 have died and thousands are wounded on both sides;
• Hundreds of Israelis are being held hostage by Hamas, including women, children and the elderly;
• Israeli captives and their captors have been killed in airstrikes since the weekend, according to Hamas;
• Israeli civilians have been gunned down in towns, along roads and at a techno music festival being held in the desert near Gaza;
• Rishi Sunak is chairing a COBRA emergency response meeting;
• More than 123,000 people have been displaced in Gaza, UN says.

Israel-Hamas War - watch special programme on Sky News tonight at 9pm.

At least 700 people have reportedly been killed in Israel and 560 have died in Gaza as Israel retaliated with airstrikes in an operation which has been dubbed "Swords of Iron".

On Monday, Hamas's armed wing claimed four Israeli captives and their Hamas captors have been killed in strikes since the beginning of the attack.

An Israeli air strike also killed 19 people, including women and children, said Talat Barhoum, a doctor at the local Al Najjar Hospital in Gaza.

Inside the Gaza Strip, more than 1,000 targets had been hit, the IDF said earlier, including airstrikes that levelled much of the town of Beit Hanoun in the northeast corner.

Meanwhile, the IDF said on Monday that it thought the situation would be in "a better place".

Mr Spielman said Hamas fighters have "embedded themselves" in Israel, with one individual coming out of hiding and shooting in one community.

"There are potentially serious numbers of terrorists that are in hiding," he said.

"We are battling an enemy that is more similar to ISIS than any other type of enemy that the world has encountered in many, many years."

A major question remains over whether Israel will launch a ground assault into Gaza, a move that in the past has brought increased casualties.

When questioned on this, Mr Spielman said: "I can tell you that we're weighing the situation very carefully.

"We're going to need to take a deep breath, because this is going to take a significant period of time."

'Darkest day in our history'

The Israeli rescue service Zaka said its paramedics removed about 260 bodies from a music festival attended by thousands that came under attack, but the number killed may rise.

Video on social media and Israeli news outlets showed dozens of festival-goers running through an open field as gunshots rang out. Many hid in nearby fruit orchards or were gunned down as they fled.

"It's the darkest day in our history," Lieutenant Colonel Jonathan Conricus, spokesperson for the IDF, said.

"You could say it's 9/11 and Pearl Harbor together for us," he told Fox News.

During their rampage through southern Israel, militants dragged back into Gaza dozens of captives.

Authorities are still trying to determine how many civilians and soldiers were seized by Hamas fighters and taken back to Gaza.

From videos and witnesses, the captives are known to include women, children and the elderly.

Senior Hamas official Mousa Abu Marzouk told Arabic language news outlet al Ghad on Sunday that his group was holding more than 100 people captive.

He said they would not be released until all Palestinian prisoners in Israeli jails were freed.

Read more:
Haunting messages left by Israelis taken hostage
What is Hamas - and why has it chosen now to strike?
British man serving in Israeli army killed in Hamas attack

At the UN, the United States called on all 15 members of the security council to strongly condemn "heinous terrorist attacks committed by Hamas".

How Hamas carried out deadly Israel attack

Meanwhile, Prime Minister Rishi Sunak was due to chair a COBRA emergency response committee meeting to discuss the situation in Israel.

"We already have a very long-standing relationship with Israel, we are one of their strongest allies, we've provided in the past the kinds of equipment that they've used to defend themselves over the past couple of days," Mr Sunak told reporters in Nottinghamshire.

"And as I said to the prime minister (Benjamin Netanyahu), we will continue to provide, whether that's diplomatic, intelligence or security support as they need."