The United Nations has warned of a “disaster” in Gaza as US Secretary of State Antony Blinken vowed to help defend Israel “as long as America exists” on a high-profile visit to the country.

However, speaking at a military base in Tel Aviv, Mr Blinken, appeared to urge caution in Israel’s retaliation against Gaza, which has decimated neighbourhoods and killed hundreds of civilians.

Israel said it has dropped more than 6,000 bombs on the Gaza Strip by Israel since fighting began on Saturday.

Israeli Minster of Foreign Affairs, Eli Cohen welcomes US Secretary of State Antony Blinken in Jerusalem, Israel. .

The UN warned that the situation in Gaza is "dire", with food and water running out.

Israel has said it will not end a siege which blocks any essential supplies from entering Gaza until its hostages are released. The government said earlier on Thursday that it had informed 95 families that their relatives had been kidnapped and taken into Gaza during Saturday’s attacks.

The death toll on both sides is growing and in Israel now stands at more than 1,300, while the Health Ministry in Gaza said that 1,417 Palestinians have been killed, including 447 children, while 6,268 have been wounded since Saturday.

Mr Blinken’s visit, which followed one day after a trip by foreign secretary James Cleverly, came as the UK launched repatriation flights to evacuate British citizens from the war-hit country.

“Too often in the past, leaders have equivocated in the face of terrorist attacks against Israel and its people,” Mr Blinken said, standing next to Israeli prime minister Benjamin Netanyahu. “This is - this must be - a moment for moral clarity.”

Mr Blinken said he had spoken to Mr Netanyahu about Israel’s approach to defence in the wake of the Hamas attacks.

“The value that we place on human life and human dignity - that’s what makes us who we are,” he said. “That’s why it’s important to take every possible precaution to prevent harming civilians. And that’s why we mourn the loss of every innocent life.”

A ground assault looks imminent as Israel amasses troops on the border with Gaza. It is thought any kind of ground attack is likely to target the vast network of tunnels in Gaza, an underground network known as “Gaza’s Metro.” Gaza is one of the most densely populated places in the world.

The Foreign Office said vulnerable British nationals would be prioritised for flights out of Israel, which are believed to cost £300 per ticket. BA and Virgin flights to and from the airport are currently suspended. El Al - the Israeli carrier - continues to operate flights to the UK.

The Government said those eligible to leave would be contacted directly and British nationals should not go to airports unless they are called to.

Adnan Abu Hasna, a spokesman for UNRWA, the UN agency that helps Palestinian refugees, warned that hospitals were running out of fuel to keep backup generators going, after Gaza’s only power plant ran out of energy on Wednesday.

“We have four-five days worth supply of fuel left” to keep aid operations going, he said. “The shelling is not stopping.

“We are facing a huge disaster."

Local people in Gaza have reported that Israel has dropped leaflets explaining why it is “taking action”. The leaflet warns residents to go to shelters and says buildings where Hamas are operating will be destroyed.

Herzi Halevi, the Israeli military chief of staff, acknowledged Israeli army failures in responding to Saturday’s attacks.

“The Israel Defence Forces (IDF) is responsible for the security of the country and its citizens, and on Saturday morning, in the area surrounding the Gaza Strip” the army did not fulfill this responsibility, he said. “We will learn, we will investigate, but now is the time for war.”

Former head of MI6 Sir Alex Younger has said Israel’s failure to pre-empt Hamas’ attack stemmed from a “failure of imagination”.

Speaking in a radio interview, Sir Alex said: “I would say two things. The first is the really big failures that are labelled as intelligence failures… are in fact failures of imagination. 9/11 classically was that. The assumption was not that we were vulnerable to anything in terms of this type of attack. The assumption was that it essentially wasn’t possible.

“Absolutely, in this case, the received assumption, demonstrated through (Israel’s) actions, particularly the deployment of the IDF, make it really clear that the received assumption was that the threat from Hamas in Gaza was quiescent.”

He said Israel risks walking into a “trap” if it launches a full-scale ground invasion of Gaza, and warned that Israel should not “do what your enemy wants you to do”.

Sir Alex said: “I absolutely understand and endorse Israel’s right to defend themselves in these circumstances and indeed to restore the credibility of those defences so that sense of psychological safety can be restored to the people.

“I also think, by the way, Hamas will be taken aback by the extent of their success. I don’t believe that they thought they would break through this far and fast and 100 hostages I suspect has gone wildly beyond anything they thought they might achieve.

“But here’s the thing, you shouldn’t do what your enemy wants you to do and it’s really obvious now that Hamas are essentially laying a trap for Israel and will be well pleased if Israel commits itself to an open-ended, full-scale ground invasion of Gaza.

“Because of the scale and intensity of conflict that that would entail and the loss of innocent life that would inevitably follow, and the radicalisation that would engender and the extent to which it would put Israel’s allies and partners in the region in an impossible position.

“These are all things that Hamas wants. This isn’t about actions, it’s about reactions.

“Israel is going to have to do strikes into Gaza to demonstrate its intent to assuage the expectations of the Israeli people but there is not, fundamentally, at the end of this a military solution to this problem.

“You cannot kill all the terrorists without creating more terrorists.”

UN warns of ‘disaster’ in Gaza as US secretary of state Antony Blinken vows to defend Israel ‘as long as America exists’