UNITED NATIONS — The new British prime minister, Keir Starmer, took the international stage at the United Nations General Assembly on Thursday for the first time with a message: His nation is returning to “responsible global leadership.”

The Labour Party leader, who won a landslide election victory in July, told the annual gathering of world leaders that with him as prime minister, “the U.K. will lead again tackling climate change at home and internationally, and restoring our commitment to international development.”

Working with other nations, Mr. Starmer said, Britain will also tackle conflicts from Gaza and the West Bank to Ukraine and Sudan where immediate cease-fires are urgently needed.

He said nations must also work together “to make the world less dangerous.”

“We have to face some hard truths,” the prime minister said. “The institutions of peace are struggling, underfunded, under pressure and outpoliticized.”

He said the entire global system of arms control and combating the proliferation of weapons which has been constructed over decades “has begun to fall away” and needs global action.

“We will also change how the U.K. does things,” Mr. Starmer said. “Moving from the paternalism of the past towards partnership for the future — listening a lot more, speaking a lot less.”

He said the U.K. will also be offering other countries “game-changing British expertise,” and will work together with nations “in a spirit of equal respect.”

Mr. Starmer told assembled ministers and diplomats that “a sense of fatalism has taken hold” in an age people describe as polarized and full of impunity and instability.

“Well, our task is to say: No. We won’t accept this slide into greater and greater conflict, instability and injustice,” he said. “Instead, we will do all we can to change it.”

Associated Press