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 Israeli government 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, if not wholly unexpected, shift in his position, reflecting the intense political pressure his government has faced as the public and lawmakers in his own Labour Party recoil from images of starving children in Gaza.