Prime Minister Keir Starmer announced on Tuesday that Britain would recognize the state of Palestine in September if Israel does not agree to a cease-fire with Hamas, pouring pressure on the Israelis to halt a war that has put Gaza on the brink of famine.

Mr. Starmer’s announcement, which came after an emergency meeting of his cabinet, is a sharp shift in his position, reflected the intense political pressure his government has faced as the British public recoils from images of starving children in Gaza.

Mr. Starmer said recognition would not be immediate but would come as part of a broader European effort to end the ruinous war between Israel and Hamas. Britain followed in the steps of France, which announced last week that it would recognize an independent Palestinian state in September.

Britain’s decision will deepen Israel’s diplomatic isolation after it abandoned a truce with Hamas in March and resumed its military offensive in Gaza. It also carries significant symbolic weight, given Britain’s diplomatic stature and history in the Middle East.

Britain is the second member of the Group of 7 nations — also including the United States, Canada, Germany, Japan and Italy — to take this step. It played a critical role in the creation of the state of Israel by declaring in 1917 that it supported the establishment of a “national home for the Jewish people” in what was then Palestine.

Mr. Starmer had been ambivalent about recognizing a Palestinian state, several officials said, in part because he viewed it as a “performative” gesture that would not change the situation on the ground and could, in fact, complicate efforts to negotiate a cease-fire between Israel and Hamas.

But a chorus of warnings about rising starvation in Gaza, after Israeli restrictions on the delivery of food, changed his calculation. More than 250 lawmakers, including many from his own Labour Party, signed a letter to Mr. Starmer and the foreign secretary, David Lammy, urging Britain to recognize a Palestinian state at a U.N. conference this week that is devoted to the two-state solution.

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