President Volodymyr Zelensky of Ukraine on Monday urged those gathering for the United Nations General Assembly in New York to place “real, powerful pressure on Russia” to end the war it began more than three years ago. Mr. Zelensky posted the message on social media as, he said, rescue efforts were underway after Russian strikes on Zaporizhzhia and the Donetsk, Dnipro, Sumy, Kyiv, Kharkiv and Kherson regions. His message came as Karoline Leavitt, the White House press secretary, said President Trump would meet with Mr. Zelensky on Tuesday in New York. Mr. Zelensky has expressed some optimism about U.S.-led peace efforts. Still, this year’s General Assembly is “the fourth time in a row that Russia accompanies one of the world’s highest-level annual diplomatic events with killings,” he posted.