“One miscalculation, one miscommunication, one mistake could lead to the unthinkable: a full-scale regional conflict that would be devastating for all involved and the rest of the world,” Mr. Guterres told the U.N. Security Council. “The moment of maximum peril must be a time for maximum restraint.”

But Prime Minister Benjamin Netanyahu has said that Israel will not bow to external pressure. He declared on Wednesday, after meeting with the British and German foreign ministers, that Israel will “do everything necessary to defend itself” and that “we will make our own decisions.”

Iranian leaders have vowed in recent days to strike back even more forcefully at Israel if it attacks Iran. Maj. Gen. Ahmad Haghtalab, the Islamic Revolutionary Guards Corps commander in charge of protecting Iran’s nuclear sites, said on Thursday that if Israel were to hit one of those sites, “the hands are on the trigger” to strike Israeli nuclear facilities, according to Iranian state news media.

The rising tensions between Israel and Iran came as the U.N. Security Council weighed on Thursday whether to back a Palestinian bid to become a full-member state of the United Nations.

The United States vetoed the measure, casting the only vote against it in the 15-member Council. Twelve nations voted in favor, and two abstained.

A “no” by any of the five permanent members stops any Security Council action. Among those five, France, Russia and China voted for the resolution to elevate the Palestinians’ status, and Britain abstained.

At the United Nations, Palestine is currently granted the lesser status of observer, like the Holy See.

But with more than 33,000 Palestinians killed in Israel’s military offensive in Gaza, according to local health officials, and many more left homeless and suffering from extreme hunger, some argue that U.N. recognition of a Palestinian state is long overdue. The push for recognition also comes as Israel is expanding settlements in the occupied West Bank.

Israel’s government was strongly opposed to the U.N. resolution, with its foreign minister, Mr. Katz, calling it a “shameful proposal.”