The US has for the sixth time vetoed a draft resolution at the United Nations Security Council that would have demanded an immediate and permanent ceasefire in Gaza and the release of hostages.
US deputy Middle East envoy Morgan Ortagus said the text did not go far enough in condemning Hamas or recognise Israel's right to defend itself.
All 14 other members of the Security Council voted in favour of the draft resolution - which described the humanitarian situation in Gaza as "catastrophic" and called on Israel to lift all aid restrictions.
It comes as the UN's humanitarian office warns that the last lifelines for civilians are collapsing in Gaza City as Israel expands its military offensive.
On the global stage, Israel and its closest ally look increasingly isolated.
Speaking prior to the vote, Ortagus said Washington's opposition to the resolution should "come as no surprise".
"It fails to condemn Hamas or recognise Israel's right to defend itself, and it wrongly legitimises the false narratives benefitting Hamas, which have sadly found currency in this council," she said.
After the vote, UN members reacted swiftly to express their disappointment.