Russia and China have blocked a US draft resolution put to the UN which for the first time called for a ceasefire and hostage releases in Gaza.
While there have been previous attempts by other countries to call for a ceasefire, the US text marked a hardening of its stance towards Israel.
But Russia and China used their veto. Moscow called the text "hypocritical".
The move by the US, Israel's key ally, comes at a time of growing tensions between them.
Washington has made clear that it expects Israel to lessen the intensity of its offensive in Gaza, where the Hamas-run health ministry says at least 31,988 people - mainly women and children - have been killed since the war began on 7 October.
It has also said it would not support an Israeli attack on the city of Rafah without a plan to protect civilians there, and has urged Israel to allow more humanitarian aid into Gaza.
Israel's Prime Minister, Benjamin Netanyahu, has said that Israel will go ahead with a planned ground assault on Rafah, even without the support of its key ally.
The US Secretary of State, Antony Blinken, in Tel Aviv for talks, said such an operation was not the answer.
"It risks killing more civilians, it risks wreaking greater havoc with the provision of humanitarian assistance, it risks further isolating Israel around the world and jeopardising this long-term security and standing," he said.
The US - one of five permanent members of the Security Council with the power of veto - has previously blocked resolutions calling for a ceasefire, saying such a move would be wrong while delicate negotiations for a truce and hostage releases were continuing between Israel and Hamas.
But on Friday it publicly changed its position, in a carefully-worded draft.
"The Security Council," the text read, "determines the imperative of an immediate and sustained ceasefire", adding "and towards that end unequivocally supports ongoing international diplomatic efforts to secure such a ceasefire in connection with the release of all remaining hostages".
In doing so, the US linked its support for a ceasefire to the release of the Israeli hostages - 253 - held by Hamas.
Although Russia and China vetoed the draft, 11 countries on the 15-member council voted in favour of it. Algeria voted against it and Guyana abstained.
Early on Saturday, a vote on a new text calling for a ceasefire was postponed until Monday, diplomats told the AFP and Reuters news agencies.
Before Friday's vote, Russia's ambassador to the UN, Vassily Nebenzia, criticised the text as "exceedingly politicised", accusing it of doing nothing to avert Israel's planned assault on Rafah.
More than half of Gaza's 2.3 million Palestinians are sheltering in the southern city, where Israel says Hamas leaders are hiding and Hamas battalions still operate.
The US ambassador to the UN, Linda Thomas-Greenfield, called Russia and China's action "deeply, deeply cynical".
"Russia and China simply did not want to vote for a resolution that was penned by the United States, because it would rather see us fail than see this Council succeed," she said.
Speaking after talks with Mr Netanyahu, Mr Blinken said the US was trying to show the international community "a sense of urgency".
A ceasefire tied to the release of hostages, he said, was "something that everyone, including the countries that veto the resolution should have been able to get behind".
French President Emmanuel Macron said his country would now work on an alternative resolution.
"What's important to note is that the United States has changed its position, and shown its will to defend, very clearly now, a ceasefire," Mr Macron said.
"For a long time, the Americans were reticent. That reticence is now gone."
