The first senior Trump administration official was expected to visit Ukraine, a day after Russia released an American prisoner in a development that President Trump called a positive signal for cease-fire talks.

Treasury Secretary Scott Bessent’s trip comes amid anxiety in Kyiv and among American allies about whether U.S. support for the Ukrainian war effort will be maintained now that Mr. Trump has returned to the White House.

The Trump administration has already sought an arrangement for the United States to secure rights to Ukrainian natural resources, including rare earth minerals, as a guarantee for further U.S. assistance.

Mr. Trump said in a post on Truth Social on Tuesday that he was sending Mr. Bessent to Ukraine because “this war must and will end soon — too much death and destruction.”

Mr. Trump, who has made American spending in a variety of areas a focus of the early days of his new administration, also wrote that the visit would touch on American assistance to Ukraine. The United States, he wrote, had spent billions of dollars “with too little to show” for it.

President Volodymyr Zelensky of Ukraine said he welcomed the visit by Mr. Bessent. “We are already prepared for meetings with representatives of the United States — negotiations will begin soon,” Mr. Zelensky in his evening address to Ukrainians on Tuesday.