The vote came after weeks of urgent discussions that had highlighted deep divisions in the UN's most powerful body about how to respond to the bloodshed in Gaza.
The United States vetoed a UN Security Council resolution that sought to explore ways to ensure "international protection" for Palestinian civilians as the council prepared Friday to vote on a competing US proposal to condemn Hamas over the recent escalation of violence in Gaza.
The vote came after weeks of urgent discussions that had highlighted deep divisions in the UN's most powerful body about how to respond to the bloodshed.
In vetoing the Arab-backed measure drafted by Kuwait, US Ambassador Nikki Haley called it "grossly one-sided" for demanding that the Israeli military halt "the use of any excessive, disproportionate and indiscriminate force" while not mentioning Hamas, the militant group that controls Gaza.
"This resolution is wildly inaccurate in its characterisation of recent events in Gaza" and "would harm any efforts toward peace," she said.
But Kuwaiti Ambassador Mansour Al-Otaibi said the veto stood to exacerbate the problems in Gaza.
"It will increase the sentiment of despair among the Palestinians," he said.
The proposed US resolution, meanwhile, deletes the reference to Israeli force and protecting Palestinians. Instead, it demands that Hamas and other Palestinian militant groups stop "all violent activity and provocative actions" in Gaza.
In two months of mass protests at the Gaza border, at least 115 Palestinians have been killed and thousands wounded by Israeli military fire. Israel says its troops are defending its border and accuses Hamas of trying to attack under the cover of the protest.
In the latest protests on Friday, a 21-year old woman was killed.
Hamas and a smaller Islamic militant group bombarded southern Israel with rockets and mortars Tuesday, and Israel responded by striking targets throughout Gaza. Hamas said Wednesday it had agreed to a cease-fire with Israel.
The vetoed Kuwaiti draft resolution expressed "grave concern" at the increased violence and deteriorating situation in the Palestinian territories and called for urgent steps to ensure a "durable and fully respected cease-fire."
It asked UN Secretary-General Antonio Guterres for a written report within 60 days on ways to ensure "the safety, protection and well-being of the Palestinian civilian population under Israeli occupation," including recommendations about "an international protection mechanism." The measure also urged humanitarian access and sought "tangible steps" toward reconciliation between different Palestinian factions.
Israeli Ambassador Danny Danon called the draft biased and "not worthy of consideration by the Security Council." Neither Israel nor the Palestinians are members of the council.
At Kuwait's request, the council has held multiple emergency meetings on the border clashes. The US called an emergency session Wednesday on the barrage of rockets and mortars the day prior.
Israel and Hamas are bitter enemies and have fought three wars since the Islamic group seized control of Gaza in 2007.