The official line is "it would interfere with negotiations to release abducted hostages".

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The US was the sole vote against a ceasefire in the UN Security Council today. The vote was largely being pushed by Arab countries in the Middle East.

The Security Council vote on the resolution, backed by Arab states, had 13 in favor and one — the U.S. — against, while the United Kingdom abstained.

Several foreign ministers of Arab countries that have been pushing for a cease-fire met U.S. Secretary of State Antony Blinken in Washington shortly after the U.S. veto.

The US voted against the ceasefire largely because it felt it's recommendations for the resolution language were ignored.

"We propose language ... that would have reinforced the life-saving diplomacy we have undertaken since Oct. 7, increased opportunities for humanitarian aid to enter Gaza, encourage the release of hostages and the resumption of humanitarian pauses and laid a foundation for a durable peace," Wood said.

"Unfortunately, nearly all of our recommendations were ignored."

The US also wanted for the resolution to denounce the Hamas attack on October 7th, which was also left out:

Wood said the resolution's authors declined to condemn Hamas' Oct. 7 attack that killed 1,200 people, including women, children and elderly.

Personally, I agree with the US here. I don't think a ceasefire with no conditions on it is going to be beneficial to the long term resolution of the war. There needs to be action from Hamas to show they are willing to engage and negotiation in talks in good-faith, and conditions for them to continue to not engage. Israel sitting idly by while Hamas is allowed to continue operating on their border just means that a similar attack will happen again. From a national security prospective of Israel, they too need to gain something from a ceasefire.

But long lasting peace in the region will only come when both Hamas & the current Israeli government are no longer in power.

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https://www.politico.com/news/2023/11/18/biden-op-ed-gaza-cease-fire-00127935

This is a good summary of the White House's position against a ceasefire. They believe that Hamas was the sole aggressor in this war and is ideologically devoted to Israel's destruction. Thus a permanent peace cannot be made with it, and a ceasefire would only delay the inevitable resumption of war. Thus, Israel should be allowed to destroy Hamas completely, so that permanent peace can be achieved. TLDR: the US believes a permanent peace can only be achieved with the total destruction of Hamas

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UK Response: Explaining the UK’s abstention from the draft resolution, Ambassador Barbara Woodward said her country could not vote in favour of a resolution that fails to condemn the atrocities Hamas committed on innocent Israeli civilians on 7 October. “Calling for a ceasefire ignores the fact that Hamas has committed acts of terror and is still holding civilians hostage,” she said, noting that Israel needs to be able to address the threat posed by Hamas and it needs to do so in a manner that abides by international humanitarian law. She reiterated the importance of working meaningfully towards a two-State solution “which delivers statehood for the Palestinians, security for Israel and peace for people on both sides.” US Response: The US engaged in good faith on the text, said Deputy Permanent Representative Robert A. Wood, that would increase opportunities for hostage release and more aid to reach Gaza. “Unfortunately, nearly all of our recommendations were ignored” leading to an “imbalanced resolution that was divorced from reality that would not move the needle forward on the ground in any concrete way. And so, we regretfully could not support it." He said the US still could not understand why the resolution’s authors declined to include language condemning “Hamas’s horrific terrorist attack” on Israel, of 7 October. It killed people from a range of nationalities, subjecting many to “obscene sexual violence.” He said he had explained earlier in the day why an unconditional ceasefire would simply be “dangerous” and leave Hamas in place, able to attack again. It was “a recipe for disaster for Israel, for Palestinians and for the entire region”. Any ceasefire leaving Hamas in control would also deny Palestinians the chance to build something better for themselves, he added. Sauce: https://news.un.org/en/story/2023/12/1144562 Edit: formatting More on reddit.com